diff --git a/resources/ui_layout/default/filament.ui b/resources/ui_layout/default/filament.ui
index 76a269f9fa4..60f105f24c6 100644
--- a/resources/ui_layout/default/filament.ui
+++ b/resources/ui_layout/default/filament.ui
@@ -20,7 +20,7 @@ group:Temperature °C
 group:Filament properties
 	setting:width$7:filament_type
 	setting:filament_soluble
-    setting:filament_shrink
+	setting:filament_shrink
 	setting:filament_max_overlap
 group:Print speed override
 	setting:filament_max_speed
@@ -30,18 +30,30 @@ group:Print speed override
 page:Cooling:time
 group:Fan speed - default
 	setting:label$Run the fan at default speed when possible:fan_always_on
+	line:Disable fan for the first
+		setting:width$5:label$_:sidetext_width$7:disable_fan_first_layers
+		setting:width$5:label_width$12:full_fan_speed_layer
+	end_line
 	setting:min_fan_speed
+	line:Perimeter fan speed
+		setting:label$:perimeter_fan_speed
+		setting:label_width$12:label$External:external_perimeter_fan_speed
+	end_line
+	setting:overhang_perimeter_fan_speed
+	setting:infill_fan_speed
+	line:Solid Infill fan speed
+		setting:label$:solid_infill_fan_speed
+		setting:label_width$12:label$Top:top_fan_speed
+	end_line
+	line:Support Material fan speed
+		setting:label$:support_material_fan_speed
+		setting:label_width$12:label$Support Interface:support_material_interface_fan_speed
+	end_line
 	line:Bridges fan speed
 		setting:label$:bridge_fan_speed
-		setting:label$Infill bridges:bridge_internal_fan_speed
-	end_line
-	setting:top_fan_speed
-	setting:external_perimeter_fan_speed
-	setting:support_material_interface_fan_speed
-	line:Disable fan for the first
-		setting:label$_:sidetext_width$12:disable_fan_first_layers
-		setting:full_fan_speed_layer
+		setting:label_width$12:label$Infill bridges:bridge_internal_fan_speed
 	end_line
+	setting:gap_fill_fan_speed
 group:Short layer time - began to increase base fan speed
 	setting:fan_below_layer_time
 	setting:label$Max fan speed:max_fan_speed
diff --git a/resources/ui_layout/example/filament.ui b/resources/ui_layout/example/filament.ui
index 76a269f9fa4..60f105f24c6 100644
--- a/resources/ui_layout/example/filament.ui
+++ b/resources/ui_layout/example/filament.ui
@@ -20,7 +20,7 @@ group:Temperature °C
 group:Filament properties
 	setting:width$7:filament_type
 	setting:filament_soluble
-    setting:filament_shrink
+	setting:filament_shrink
 	setting:filament_max_overlap
 group:Print speed override
 	setting:filament_max_speed
@@ -30,18 +30,30 @@ group:Print speed override
 page:Cooling:time
 group:Fan speed - default
 	setting:label$Run the fan at default speed when possible:fan_always_on
+	line:Disable fan for the first
+		setting:width$5:label$_:sidetext_width$7:disable_fan_first_layers
+		setting:width$5:label_width$12:full_fan_speed_layer
+	end_line
 	setting:min_fan_speed
+	line:Perimeter fan speed
+		setting:label$:perimeter_fan_speed
+		setting:label_width$12:label$External:external_perimeter_fan_speed
+	end_line
+	setting:overhang_perimeter_fan_speed
+	setting:infill_fan_speed
+	line:Solid Infill fan speed
+		setting:label$:solid_infill_fan_speed
+		setting:label_width$12:label$Top:top_fan_speed
+	end_line
+	line:Support Material fan speed
+		setting:label$:support_material_fan_speed
+		setting:label_width$12:label$Support Interface:support_material_interface_fan_speed
+	end_line
 	line:Bridges fan speed
 		setting:label$:bridge_fan_speed
-		setting:label$Infill bridges:bridge_internal_fan_speed
-	end_line
-	setting:top_fan_speed
-	setting:external_perimeter_fan_speed
-	setting:support_material_interface_fan_speed
-	line:Disable fan for the first
-		setting:label$_:sidetext_width$12:disable_fan_first_layers
-		setting:full_fan_speed_layer
+		setting:label_width$12:label$Infill bridges:bridge_internal_fan_speed
 	end_line
+	setting:gap_fill_fan_speed
 group:Short layer time - began to increase base fan speed
 	setting:fan_below_layer_time
 	setting:label$Max fan speed:max_fan_speed
diff --git a/src/libslic3r/ExtrusionEntity.hpp b/src/libslic3r/ExtrusionEntity.hpp
index 4f1116d4a71..73fca1ba17d 100644
--- a/src/libslic3r/ExtrusionEntity.hpp
+++ b/src/libslic3r/ExtrusionEntity.hpp
@@ -52,7 +52,7 @@ enum ExtrusionRole : uint16_t {
 };
 */
 enum ExtrusionRole : uint8_t {
-    erNone,
+    erNone, // erNone needs to be 0 (for cooling and everything that use the role as index)
     erPerimeter,
     erExternalPerimeter,
     erOverhangPerimeter,
diff --git a/src/libslic3r/GCode.cpp b/src/libslic3r/GCode.cpp
index 529d2c642cf..fc917dcea0b 100644
--- a/src/libslic3r/GCode.cpp
+++ b/src/libslic3r/GCode.cpp
@@ -5386,8 +5386,38 @@ double_t GCode::_compute_speed_mm_per_sec(const ExtrusionPath& path, double spee
     return speed;
 }
 
+
+void GCode::cooldown_marker_init() {
+    if (!_cooldown_marker_speed[ExtrusionRole::erExternalPerimeter].empty()) {
+        std::string allow_speed_change = ";CM_extrude_speed;_EXTRUDE_SET_SPEED";
+        //only change speed on external perimeter (and similar) speed if really necessary.
+        std::string maybe_allow_speed_change = ";CM_extrude_speed_external;_EXTRUDE_SET_SPEED_MAYBE";
+        _cooldown_marker_speed[erNone] = "";
+        _cooldown_marker_speed[erPerimeter] = allow_speed_change;
+        _cooldown_marker_speed[erExternalPerimeter] = maybe_allow_speed_change;
+        _cooldown_marker_speed[erOverhangPerimeter] = "";
+        _cooldown_marker_speed[erInternalInfill] = allow_speed_change;
+        _cooldown_marker_speed[erSolidInfill] = allow_speed_change;
+        _cooldown_marker_speed[erTopSolidInfill] = allow_speed_change;
+        _cooldown_marker_speed[erIroning] = maybe_allow_speed_change;
+        _cooldown_marker_speed[erBridgeInfill] = "";
+        _cooldown_marker_speed[erInternalBridgeInfill] = maybe_allow_speed_change;
+        _cooldown_marker_speed[erThinWall] = maybe_allow_speed_change;
+        _cooldown_marker_speed[erGapFill] = allow_speed_change;
+        _cooldown_marker_speed[erSkirt] = allow_speed_change;
+        _cooldown_marker_speed[erSupportMaterial] = allow_speed_change;
+        _cooldown_marker_speed[erSupportMaterialInterface] = maybe_allow_speed_change;
+        _cooldown_marker_speed[erWipeTower] = allow_speed_change;
+        _cooldown_marker_speed[erMilling] = "";
+        _cooldown_marker_speed[erCustom] = maybe_allow_speed_change;
+        _cooldown_marker_speed[erMixed] = maybe_allow_speed_change;
+    }
+}
+
+
 std::string GCode::_before_extrude(const ExtrusionPath &path, const std::string &description_in, double speed) {
     std::string gcode;
+    gcode.reserve(512);
     std::string description{ description_in };
 
 
@@ -5730,20 +5760,10 @@ std::string GCode::_before_extrude(const ExtrusionPath &path, const std::string
 
     std::string comment;
     if (m_enable_cooling_markers) {
-        if(path.role() == erInternalBridgeInfill)
-            gcode += ";_BRIDGE_INTERNAL_FAN_START\n";
-        else if (is_bridge(path.role()))
-            gcode += ";_BRIDGE_FAN_START\n";
-        else if (ExtrusionRole::erTopSolidInfill == path.role())
-            gcode += ";_TOP_FAN_START\n";
-        else if (ExtrusionRole::erSupportMaterialInterface == path.role())
-            gcode += ";_SUPP_INTER_FAN_START\n";
-        else
-            comment = ";_EXTRUDE_SET_SPEED";
-        if (path.role() == erExternalPerimeter)
-            comment += ";_EXTERNAL_PERIMETER";
-        if (path.role() == erThinWall)
-            comment += ";_EXTERNAL_PERIMETER";
+        // Send the current extrusion type to Coolingbuffer
+        gcode += ";_EXTRUDETYPE_"; gcode += char('A' + path.role()); gcode += "\n";
+        // comment to be on the same line as the speed command.
+        comment = GCode::_cooldown_marker_speed[path.role()];
     }
     // F     is mm per minute.
     // speed is mm per second
@@ -5753,17 +5773,10 @@ std::string GCode::_before_extrude(const ExtrusionPath &path, const std::string
 }
 std::string GCode::_after_extrude(const ExtrusionPath &path) {
     std::string gcode;
-    if (m_enable_cooling_markers)
-        if (path.role() == erInternalBridgeInfill)
-            gcode += ";_BRIDGE_INTERNAL_FAN_END\n";
-        else if (is_bridge(path.role()))
-            gcode += ";_BRIDGE_FAN_END\n";
-        else if (ExtrusionRole::erTopSolidInfill == path.role())
-            gcode += ";_TOP_FAN_END\n";
-        else if (ExtrusionRole::erSupportMaterialInterface == path.role())
-            gcode += ";_SUPP_INTER_FAN_END\n";
-        else
-            gcode += ";_EXTRUDE_END\n";
+    if (m_enable_cooling_markers) {
+        // Notify Coolingbuffer that the current extrusion end.
+        gcode += ";_EXTRUDE_END\n";
+    }
 
     if (path.role() != ExtrusionRole::erGapFill ) {
         m_last_notgapfill_extrusion_role = path.role();
diff --git a/src/libslic3r/GCode.hpp b/src/libslic3r/GCode.hpp
index b7848ab3e1c..f3f9d1f5392 100644
--- a/src/libslic3r/GCode.hpp
+++ b/src/libslic3r/GCode.hpp
@@ -155,7 +155,9 @@ class GCode : ExtrusionVisitorConst  {
         m_silent_time_estimator_enabled(false),
         m_last_obj_copy(nullptr, Point(std::numeric_limits<coord_t>::max(), std::numeric_limits<coord_t>::max())),
         m_last_too_small(ExtrusionRole::erNone)
-        {}
+    {
+        cooldown_marker_init();
+    }
     ~GCode() = default;
 
     // throws std::runtime_exception on error,
@@ -527,6 +529,11 @@ class GCode : ExtrusionVisitorConst  {
     friend class Wipe;
     friend class WipeTowerIntegration;
     friend class PressureEqualizer;
+
+    //utility for cooling markers
+    static inline std::string _cooldown_marker_speed[ExtrusionRole::erCount];
+    bool cooldwon_marker_no_slowdown_section = false;;
+    static void cooldown_marker_init();
 };
 
 std::vector<const PrintInstance*> sort_object_instances_by_model_order(const Print& print);
diff --git a/src/libslic3r/GCode/CoolingBuffer.cpp b/src/libslic3r/GCode/CoolingBuffer.cpp
index 5cead49efb1..274325a70b0 100644
--- a/src/libslic3r/GCode/CoolingBuffer.cpp
+++ b/src/libslic3r/GCode/CoolingBuffer.cpp
@@ -45,20 +45,17 @@ void CoolingBuffer::reset(const Vec3d &position)
 struct CoolingLine
 {
     enum Type : uint32_t {
-        TYPE_SET_TOOL           = 1 << 0,
-        TYPE_EXTRUDE_END        = 1 << 1,
-        TYPE_BRIDGE_FAN_START   = 1 << 2,
-        TYPE_BRIDGE_FAN_END     = 1 << 3,
-        TYPE_BRIDGE_INTERNAL_FAN_START  = 1 << 4,
-        TYPE_BRIDGE_INTERNAL_FAN_END    = 1 << 5,
-        TYPE_TOP_FAN_START      = 1 << 6,
-        TYPE_TOP_FAN_END        = 1 << 7,
-        TYPE_SUPP_INTER_FAN_START = 1 << 8,
-        TYPE_SUPP_INTER_FAN_END = 1 << 9,
+        //first 5 bits are for the extrusiontype (not a flag)
+
+        TYPE_SET_TOOL           = 1 << 7,
+        TYPE_EXTRUDE_START      = 1 << 8,
+        TYPE_EXTRUDE_END        = 1 << 9,
         TYPE_G0                 = 1 << 10,
         TYPE_G1                 = 1 << 11,
+        // if adjustable, that means that the lines after that can't have their speed modified. end after a TYPE_EXTRUDE_END
         TYPE_ADJUSTABLE         = 1 << 12,
-        TYPE_EXTERNAL_PERIMETER = 1 << 13,
+        // TYPE_ADJUSTABLE_MAYBE = do not adjust this section if possible
+        TYPE_ADJUSTABLE_MAYBE   = 1 << 13,
         // The line sets a feedrate.
         TYPE_HAS_F              = 1 << 14,
         TYPE_WIPE               = 1 << 15,
@@ -71,8 +68,11 @@ struct CoolingLine
         TYPE_G3                 = 1 << 21,
         // Would be TYPE_ADJUSTABLE, but the block of G-code lines has zero extrusion length, thus the block
         // cannot have its speed adjusted. This should not happen (sic!).
-        TYPE_ADJUSTABLE_EMPTY   = 1 << 12,
+        TYPE_ADJUSTABLE_EMPTY   = 1 << 22,
     };
+    static inline ExtrusionRole to_extrusion_role(uint32_t type) {
+        return ExtrusionRole(uint8_t(type & 0x1F));
+    }
 
     CoolingLine(unsigned int type, size_t  line_start, size_t  line_end) :
         type(type), line_start(line_start), line_end(line_end),
@@ -80,7 +80,7 @@ struct CoolingLine
 
     bool adjustable(bool slowdown_external_perimeters) const {
         return (this->type & TYPE_ADJUSTABLE) && 
-               (! (this->type & TYPE_EXTERNAL_PERIMETER) || slowdown_external_perimeters) &&
+               (slowdown_external_perimeters || (!(this->type & TYPE_ADJUSTABLE_MAYBE))) &&
                this->time < this->time_max;
     }
 
@@ -330,44 +330,45 @@ std::string CoolingBuffer::process_layer(std::string &&gcode_in, size_t layer_id
 
     std::string out;
     if (flush) {
-	    auto& previous_layer_time = is_support_only ? saved_layer_time_object : saved_layer_time_support;
-	    auto my_previous_layer_time = is_support_only ? saved_layer_time_support : saved_layer_time_object;
-	    auto& my_layer_time = is_support_only ? saved_layer_time_support : saved_layer_time_object;
-	    std::vector<PerExtruderAdjustments> per_extruder_adjustments = this->parse_layer_gcode(m_gcode, m_current_pos);
-	    //save our layer time in case of unchync
-	    my_layer_time.clear();
-	    for (PerExtruderAdjustments& adj : per_extruder_adjustments) {
-	        my_layer_time[adj.extruder_id] = adj.elapsed_time_total();
-	        auto it = my_previous_layer_time.find(adj.extruder_id);
-	        if (it != my_previous_layer_time.end()) {
-	            my_previous_layer_time[adj.extruder_id] = (my_previous_layer_time[adj.extruder_id] + my_layer_time[adj.extruder_id]) / 2 - my_layer_time[adj.extruder_id];
-	        } else {
-	            my_previous_layer_time[adj.extruder_id] = 0;
-	        }
-	    }
-	    //add unsynch layer time
-	    if (!previous_layer_time.empty()) {
-	        for (PerExtruderAdjustments& adj : per_extruder_adjustments) {
-	            auto it = previous_layer_time.find(adj.extruder_id);
-	            if (it != previous_layer_time.end()) {
-	                adj.time_support = it->second;
-	            }
-	        }
-	        previous_layer_time.clear();
-	    }
-	    //add half diff with previous one, to avoid suddent change in fan speed.
-	    if (!my_previous_layer_time.empty()) {
-	        for (PerExtruderAdjustments& adj : per_extruder_adjustments) {
-	            auto it = my_previous_layer_time.find(adj.extruder_id);
-	            if (it != my_previous_layer_time.end()) {
-	                adj.time_support += it->second;
-	            }
-	        }
-	    }
-	    //compute slowdown
-	    float layer_time_stretched = this->calculate_layer_slowdown(per_extruder_adjustments);
-	    //compute fans & gcode
-	    out = this->apply_layer_cooldown(m_gcode, layer_id, layer_time_stretched, per_extruder_adjustments);
+        std::map<size_t, float>& last_different_layer_time = is_support_only ? saved_layer_time_object : saved_layer_time_support;
+        // previous_layer_time is also use at temporary store for the diff between our layer_time and its.
+        std::map<size_t, float>  previous_layer_time = is_support_only ? saved_layer_time_support : saved_layer_time_object;
+        std::map<size_t, float>& my_layer_time = previous_layer_time;
+        std::vector<PerExtruderAdjustments> per_extruder_adjustments = this->parse_layer_gcode(m_gcode, m_current_pos);
+        //save our layer time in case of unchync
+        my_layer_time.clear();
+        for (PerExtruderAdjustments& adj : per_extruder_adjustments) {
+            my_layer_time[adj.extruder_id] = adj.elapsed_time_total();
+            auto it = previous_layer_time.find(adj.extruder_id);
+            if (it != previous_layer_time.end()) {
+                previous_layer_time[adj.extruder_id] = (previous_layer_time[adj.extruder_id] + my_layer_time[adj.extruder_id]) / 2 - my_layer_time[adj.extruder_id];
+            } else {
+                previous_layer_time[adj.extruder_id] = 0;
+            }
+        }
+        //add unsynch layer time (support for object, and object for support)
+        if (!last_different_layer_time.empty()) {
+            for (PerExtruderAdjustments& adj : per_extruder_adjustments) {
+                auto it = last_different_layer_time.find(adj.extruder_id);
+                if (it != last_different_layer_time.end()) {
+                    adj.time_support += it->second;
+                }
+            }
+            last_different_layer_time.clear();
+        }
+        //add half diff with previous one, to avoid flip-flop quick change in fan speed.
+        if (!previous_layer_time.empty()) {
+            for (PerExtruderAdjustments& adj : per_extruder_adjustments) {
+                auto it = previous_layer_time.find(adj.extruder_id);
+                if (it != previous_layer_time.end()) {
+                    adj.time_support += it->second;
+                }
+            }
+        }
+        //compute slowdown
+        float layer_time_stretched = this->calculate_layer_slowdown(per_extruder_adjustments);
+        //compute fans & gcode
+        out = this->apply_layer_cooldown(m_gcode, layer_id, layer_time_stretched, per_extruder_adjustments);
         m_gcode.clear();
     }
     return out;
@@ -440,9 +441,10 @@ std::vector<PerExtruderAdjustments> CoolingBuffer::parse_layer_gcode(const std::
                     if (axis == 4) {
                         // Convert mm/min to mm/sec.
                         new_pos[4] /= 60.f;
-                        if ((line.type & CoolingLine::TYPE_G92) == 0)
+                        if ((line.type & CoolingLine::TYPE_G92) == 0) {
                             // This is G0 or G1 line and it sets the feedrate. This mark is used for reducing the duplicate F calls.
                             line.type |= CoolingLine::TYPE_HAS_F;
+                        }
                     } else if (axis == 5 || axis == 6) {
                         // BBS: get position of arc center
                         new_pos[axis] += current_pos[axis - 5];
@@ -451,15 +453,15 @@ std::vector<PerExtruderAdjustments> CoolingBuffer::parse_layer_gcode(const std::
                 // Skip this word.
                 for (; *c != ' ' && *c != '\t' && *c != 0; ++ c);
             }
-            bool external_perimeter = boost::contains(sline, ";_EXTERNAL_PERIMETER");
             bool wipe               = boost::contains(sline, ";_WIPE");
-            if (external_perimeter)
-                line.type |= CoolingLine::TYPE_EXTERNAL_PERIMETER;
             if (wipe)
                 line.type |= CoolingLine::TYPE_WIPE;
             if (boost::contains(sline, ";_EXTRUDE_SET_SPEED") && ! wipe) {
                 line.type |= CoolingLine::TYPE_ADJUSTABLE;
                 active_speed_modifier = adjustment->lines.size();
+                std::cout << "TYPE_(not)_ADJUSTABLE!\n";
+                if (boost::contains(sline, ";_EXTRUDE_SET_SPEED_MAYBE"))
+                    line.type |= CoolingLine::TYPE_ADJUSTABLE_MAYBE;
             }
             if ((line.type & CoolingLine::TYPE_G92) == 0) {
                 // G0 or G1. Calculate the duration.
@@ -561,22 +563,9 @@ std::vector<PerExtruderAdjustments> CoolingBuffer::parse_layer_gcode(const std::
                     BOOST_LOG_TRIVIAL(error) << "CoolingBuffer encountered an invalid toolchange, maybe from a custom gcode: " << sline;
             }
 
-        } else if (boost::starts_with(sline, ";_BRIDGE_FAN_START")) {
-            line.type = CoolingLine::TYPE_BRIDGE_FAN_START;
-        } else if (boost::starts_with(sline, ";_BRIDGE_FAN_END")) {
-            line.type = CoolingLine::TYPE_BRIDGE_FAN_END;
-        } else if (boost::starts_with(sline, ";_BRIDGE_INTERNAL_FAN_START")) {
-            line.type = CoolingLine::TYPE_BRIDGE_INTERNAL_FAN_START;
-        } else if (boost::starts_with(sline, ";_BRIDGE_INTERNAL_FAN_END")) {
-            line.type = CoolingLine::TYPE_BRIDGE_INTERNAL_FAN_END;
-        } else if (boost::starts_with(sline, ";_TOP_FAN_START")) {
-            line.type = CoolingLine::TYPE_TOP_FAN_START;
-        } else if (boost::starts_with(sline, ";_TOP_FAN_END")) {
-            line.type = CoolingLine::TYPE_TOP_FAN_END;
-        } else if (boost::starts_with(sline, ";_SUPP_INTER_FAN_START")) {
-            line.type = CoolingLine::TYPE_SUPP_INTER_FAN_START;
-        } else if (boost::starts_with(sline, ";_SUPP_INTER_FAN_END")) {
-            line.type = CoolingLine::TYPE_SUPP_INTER_FAN_END;
+        } else if (boost::starts_with(sline, ";_EXTRUDETYPE_") && sline.size() > 14) {
+            //set the extrusiontype
+            line.type |= CoolingLine::Type(sline[14] - 'A') | CoolingLine::Type::TYPE_EXTRUDE_START;
         } else if (boost::starts_with(sline, "G4 ")) {
             // Parse the wait time.
             line.type = CoolingLine::TYPE_G4;
@@ -797,6 +786,40 @@ float CoolingBuffer::calculate_layer_slowdown(std::vector<PerExtruderAdjustments
     return elapsed_time_total0;
 }
 
+// list of fan that can be increased (erNone is the default) via fan_below_layer_time and slowdown_below_layer_time
+// the commented ones won't buldge even is the layer time is low.
+std::vector<uint8_t> etype_can_increase_fan = {
+    ExtrusionRole::erNone,
+    ExtrusionRole::erBridgeInfill,
+    ExtrusionRole::erInternalBridgeInfill,
+    //ExtrusionRole::erTopSolidInfill,
+    //ExtrusionRole::erIroning,
+    //ExtrusionRole::erSupportMaterialInterface,
+    //ExtrusionRole::erSupportMaterial,
+    ExtrusionRole::erExternalPerimeter,
+    ExtrusionRole::erThinWall,
+    ExtrusionRole::erPerimeter,
+    ExtrusionRole::erSolidInfill,
+    ExtrusionRole::erInternalInfill,
+    ExtrusionRole::erOverhangPerimeter,
+    ExtrusionRole::erGapFill };
+// list of fan that won't be reduced in the first layers by full_fan_speed_layer (after disable_fan_first_layers)
+std::vector<uint8_t> etype_can_ramp_up_fan = {
+    ExtrusionRole::erNone,
+    //ExtrusionRole::erBridgeInfill,
+    //ExtrusionRole::erInternalBridgeInfill,
+    ExtrusionRole::erTopSolidInfill,
+    ExtrusionRole::erIroning,
+    //ExtrusionRole::erSupportMaterialInterface,
+    ExtrusionRole::erSupportMaterial,
+    ExtrusionRole::erExternalPerimeter,
+    ExtrusionRole::erThinWall,
+    ExtrusionRole::erPerimeter,
+    ExtrusionRole::erSolidInfill,
+    ExtrusionRole::erInternalInfill,
+    //ExtrusionRole::erOverhangPerimeter,
+    ExtrusionRole::erGapFill };
+
 // Apply slow down over G-code lines stored in per_extruder_adjustments, enable fan if needed.
 // Returns the adjusted G-code.
 std::string CoolingBuffer::apply_layer_cooldown(
@@ -824,75 +847,65 @@ std::string CoolingBuffer::apply_layer_cooldown(
     // Second generate the adjusted G-code.
     std::string new_gcode;
     new_gcode.reserve(gcode.size() * 2);
-    bool bridge_fan_control = false;
-    int  bridge_fan_speed = 0;
-    bool bridge_internal_fan_control = false;
-    int  bridge_internal_fan_speed = 0;
-    bool top_fan_control = false;
-    int  top_fan_speed = 0;
-    bool supp_inter_fan_control = false;
-    int  supp_inter_fan_speed = 0;
-    bool ext_peri_fan_control = false;
-    int  ext_peri_fan_speed = 0;
+    bool fan_control[ExtrusionRole::erCount];
+    int fan_speeds[ExtrusionRole::erCount];
+    int default_fan_speed[ExtrusionRole::erCount];
 #define EXTRUDER_CONFIG(OPT) m_config.OPT.get_at(m_current_extruder)
+    int min_fan_speed = EXTRUDER_CONFIG(min_fan_speed);
+    for (int i = 0; i < ExtrusionRole::erCount; i++) {
+        fan_control[i] = false;
+        fan_speeds[i] = 0;
+        default_fan_speed[i] = min_fan_speed;
+        // 0 was deprecated, replaced by 1: allow 1 to still be 0 (and it's now deprecated)
+        if (default_fan_speed[i] == 1) default_fan_speed[i] = 0;
+    }
+    default_fan_speed[ExtrusionRole::erBridgeInfill] = EXTRUDER_CONFIG(bridge_fan_speed);
+    default_fan_speed[ExtrusionRole::erInternalBridgeInfill] = EXTRUDER_CONFIG(bridge_internal_fan_speed);
+    default_fan_speed[ExtrusionRole::erTopSolidInfill] = EXTRUDER_CONFIG(top_fan_speed);
+    default_fan_speed[ExtrusionRole::erIroning] = default_fan_speed[ExtrusionRole::erTopSolidInfill];
+    default_fan_speed[ExtrusionRole::erSupportMaterialInterface] = EXTRUDER_CONFIG(support_material_interface_fan_speed);
+    default_fan_speed[ExtrusionRole::erSupportMaterial] = EXTRUDER_CONFIG(support_material_fan_speed);
+    default_fan_speed[ExtrusionRole::erExternalPerimeter] = EXTRUDER_CONFIG(external_perimeter_fan_speed);
+    default_fan_speed[ExtrusionRole::erThinWall] = default_fan_speed[ExtrusionRole::erExternalPerimeter];
+    default_fan_speed[ExtrusionRole::erPerimeter] = EXTRUDER_CONFIG(perimeter_fan_speed);
+    default_fan_speed[ExtrusionRole::erSolidInfill] = EXTRUDER_CONFIG(solid_infill_fan_speed);
+    default_fan_speed[ExtrusionRole::erInternalInfill] = EXTRUDER_CONFIG(infill_fan_speed);
+    default_fan_speed[ExtrusionRole::erOverhangPerimeter] = EXTRUDER_CONFIG(overhangs_fan_speed);
+    default_fan_speed[ExtrusionRole::erGapFill] = EXTRUDER_CONFIG(gap_fill_fan_speed);
     auto change_extruder_set_fan = [this, layer_id, layer_time, &new_gcode, 
-        &bridge_fan_control, &bridge_fan_speed, &bridge_internal_fan_control, &bridge_internal_fan_speed, 
-        &top_fan_control, &top_fan_speed,
-        &ext_peri_fan_control, &ext_peri_fan_speed,
-        &supp_inter_fan_control, &supp_inter_fan_speed]() {
-        int min_fan_speed = EXTRUDER_CONFIG(min_fan_speed);
-        bridge_fan_speed = EXTRUDER_CONFIG(bridge_fan_speed);
-        bridge_internal_fan_speed = EXTRUDER_CONFIG(bridge_internal_fan_speed);
-        top_fan_speed = EXTRUDER_CONFIG(top_fan_speed);
-        supp_inter_fan_speed = EXTRUDER_CONFIG(support_material_interface_fan_speed);
-        ext_peri_fan_speed = EXTRUDER_CONFIG(external_perimeter_fan_speed);
-        // 0 is deprecated for disable: take care of temp settings.
-        if (bridge_fan_speed == 0) bridge_fan_speed = -1;
-        if (bridge_internal_fan_speed == 0) bridge_internal_fan_speed = -1;
-        if (ext_peri_fan_speed == 0) ext_peri_fan_speed = -1;
-        if (top_fan_speed == 0) top_fan_speed = -1;
-        if (bridge_fan_speed == 1) bridge_fan_speed = 0;
-        if (bridge_internal_fan_speed == 1) bridge_internal_fan_speed = 0;
-        if (ext_peri_fan_speed == 1) ext_peri_fan_speed = 0;
-        if (top_fan_speed == 1) top_fan_speed = 0;
-        // end deprecation
-        int fan_speed_new = EXTRUDER_CONFIG(fan_always_on) ? min_fan_speed : 0;
+            &fan_control, &fan_speeds, &default_fan_speed, &min_fan_speed]()
+    {
         int disable_fan_first_layers = EXTRUDER_CONFIG(disable_fan_first_layers);
         // Is the fan speed ramp enabled?
         int full_fan_speed_layer = EXTRUDER_CONFIG(full_fan_speed_layer);
-        if (disable_fan_first_layers <= 0 && full_fan_speed_layer > 0) {
-            // When ramping up fan speed from disable_fan_first_layers to full_fan_speed_layer, force disable_fan_first_layers above zero,
-            // so there will be a zero fan speed at least at the 1st layer.
-            disable_fan_first_layers = 1;
-        }
         if (int(layer_id) >= disable_fan_first_layers) {
             int   max_fan_speed             = EXTRUDER_CONFIG(max_fan_speed);
             float slowdown_below_layer_time = float(EXTRUDER_CONFIG(slowdown_below_layer_time));
             float fan_below_layer_time      = float(EXTRUDER_CONFIG(fan_below_layer_time));
-            //if (EXTRUDER_CONFIG(cooling)) {
-                if (layer_time < slowdown_below_layer_time && fan_below_layer_time > 0) {
-                    // Layer time very short. Enable the fan to a full throttle.
-                    fan_speed_new = std::max(max_fan_speed, fan_speed_new);
-                    bridge_fan_speed = std::max(max_fan_speed, bridge_fan_speed);
-                    bridge_internal_fan_speed = std::max(max_fan_speed, bridge_internal_fan_speed);
-                    ext_peri_fan_speed = std::max(max_fan_speed, ext_peri_fan_speed); // cannot be ovveridden
-                    //top_fan_speed = std::max(max_fan_speed, top_fan_speed);
-                } else if (layer_time < fan_below_layer_time) {
-                    // Layer time quite short. Enable the fan proportionally according to the current layer time.
-                    assert(layer_time >= slowdown_below_layer_time);
-                    double t = (layer_time - slowdown_below_layer_time) / (fan_below_layer_time - slowdown_below_layer_time);
-                    if (fan_speed_new < max_fan_speed)
-                        fan_speed_new = int(floor(t * min_fan_speed + (1. - t) * max_fan_speed) + 0.5);
-                    if (bridge_fan_speed >= 0 && bridge_fan_speed < max_fan_speed)
-                        bridge_fan_speed = int(floor(t * bridge_fan_speed + (1. - t) * max_fan_speed) + 0.5);
-                    if (bridge_internal_fan_speed >= 0 && bridge_internal_fan_speed < max_fan_speed)
-                        bridge_internal_fan_speed = int(floor(t * bridge_internal_fan_speed + (1. - t) * max_fan_speed) + 0.5);
-                    if (ext_peri_fan_speed >= 0 && ext_peri_fan_speed < max_fan_speed)
-                        ext_peri_fan_speed = int(floor(t * ext_peri_fan_speed + (1. - t) * max_fan_speed) + 0.5);
-                    //if (top_fan_speed >= 0 && top_fan_speed < max_fan_speed) // cannot be ovveridden
-                    //    top_fan_speed = int(floor(t * top_fan_speed + (1. - t) * max_fan_speed) + 0.5);
+            for (int i = 0; i < ExtrusionRole::erCount; i++) {
+                fan_speeds[i] = default_fan_speed[i];
+            }
+            //if not always on, the default is "no fan" and not the min.
+            if (!EXTRUDER_CONFIG(fan_always_on)) {
+                fan_speeds[0] = 0;
+            }
+            if (layer_time < slowdown_below_layer_time && fan_below_layer_time > 0) {
+                // Layer time very short. Enable the fan to a full throttle.
+                //fan_speed_new = std::max(max_fan_speed, fan_speed_new);
+                for (size_t etype_idx = 0; etype_idx < etype_can_increase_fan.size(); etype_idx++) {
+                    uint16_t idx = etype_can_increase_fan[etype_idx];
+                    fan_speeds[idx] = std::max(max_fan_speed, fan_speeds[idx]);
                 }
-            //}
+            } else if (layer_time < fan_below_layer_time) {
+                // Layer time quite short. Enable the fan proportionally according to the current layer time.
+                assert(layer_time >= slowdown_below_layer_time);
+                double t = (layer_time - slowdown_below_layer_time) / (fan_below_layer_time - slowdown_below_layer_time);
+                for (size_t etype_idx = 0; etype_idx < etype_can_increase_fan.size(); etype_idx++) {
+                    uint16_t idx = etype_can_increase_fan[etype_idx];
+                    if (fan_speeds[idx] < max_fan_speed) // don't reduce speed if max speed is lower.
+                        fan_speeds[idx] = std::clamp(int(t * fan_speeds[idx] + (1. - t) * max_fan_speed + 0.5), 0, 255);
+                }
+            }
 
             // Is the fan speed ramp enabled?
             int full_fan_speed_layer = EXTRUDER_CONFIG(full_fan_speed_layer);
@@ -901,47 +914,50 @@ std::string CoolingBuffer::apply_layer_cooldown(
             if (int(layer_id) >= disable_fan_first_layers && int(layer_id) + 1 < full_fan_speed_layer) {
                 // Ramp up the fan speed from disable_fan_first_layers to full_fan_speed_layer.
                 float factor = float(int(layer_id + 1) - disable_fan_first_layers) / float(full_fan_speed_layer - disable_fan_first_layers);
-                fan_speed_new = std::clamp(int(float(fan_speed_new   ) * factor + 0.5f), 0, 255);
-                if (bridge_fan_speed >= 0)
-                    bridge_fan_speed = std::clamp(int(float(bridge_fan_speed) * factor + 0.5f), 0, 255);
-                if (bridge_internal_fan_speed >= 0)
-                    bridge_internal_fan_speed = std::clamp(int(float(bridge_internal_fan_speed) * factor + 0.5f), 0, 255);
+                for (size_t etype_idx = 0; etype_idx < etype_can_ramp_up_fan.size(); etype_idx++) {
+                    uint16_t idx = etype_can_ramp_up_fan[etype_idx];
+                    fan_speeds[idx] = std::clamp(int(float(fan_speeds[idx]) * factor + 0.01f), 0, 255);
+                }
             }
-            bridge_fan_control = bridge_fan_speed > fan_speed_new && bridge_fan_speed >= 0;
-            bridge_internal_fan_control = bridge_internal_fan_speed > fan_speed_new && bridge_internal_fan_speed >= 0;
-            top_fan_control = top_fan_speed != fan_speed_new && top_fan_speed >= 0;
-            supp_inter_fan_control = supp_inter_fan_speed != fan_speed_new && supp_inter_fan_speed >= 0;
-            ext_peri_fan_control = ext_peri_fan_speed != fan_speed_new && ext_peri_fan_speed >= 0;
+            //only activate fan control if the fan speed is higher than default
+            fan_control[0] = true;
+            for (size_t i = 1; i < ExtrusionRole::erCount; i++) {
+                fan_control[i] = fan_speeds[i] >= 0 && fan_speeds[i] > fan_speeds[0];
+            }
+
             // if bridge_internal_fan is disabled, it takes the value of bridge_fan_control
-            // if bridge_internal_fan_speed is too low, it takes the value of fan_speed_new
-            if (!bridge_internal_fan_control && bridge_fan_control) {
-                bridge_internal_fan_control = true;
-                if(bridge_internal_fan_speed >= 0)
-                    bridge_internal_fan_speed = fan_speed_new;
-                else
-                    bridge_internal_fan_speed = bridge_fan_speed;
+            if (!fan_control[ExtrusionRole::erInternalBridgeInfill] && fan_control[ExtrusionRole::erBridgeInfill]) {
+                fan_control[ExtrusionRole::erInternalBridgeInfill] = true;
+                fan_speeds[ExtrusionRole::erInternalBridgeInfill] = fan_speeds[ExtrusionRole::erBridgeInfill];
+            }
+
+            // if external_perimeter_fan is disabled, it takes the value of perimeter_fan
+            if (!fan_control[ExtrusionRole::erExternalPerimeter] && fan_control[ExtrusionRole::erPerimeter]) {
+                fan_control[ExtrusionRole::erExternalPerimeter] = true;
+                fan_speeds[ExtrusionRole::erExternalPerimeter] = fan_speeds[ExtrusionRole::erPerimeter];
+            }
+
+            // if top_fan is disabled, it takes the value of solid_fan
+            if (!fan_control[ExtrusionRole::erTopSolidInfill] && fan_control[ExtrusionRole::erSolidInfill]) {
+                fan_control[ExtrusionRole::erTopSolidInfill] = true;
+                fan_speeds[ExtrusionRole::erTopSolidInfill] = fan_speeds[ExtrusionRole::erSolidInfill];
             }
 
         } else {
-            bridge_fan_control = false;
-            bridge_fan_speed   = 0;
-            bridge_internal_fan_control = false;
-            bridge_internal_fan_speed = 0;
-            top_fan_control    = false;
-            top_fan_speed      = 0;
-            supp_inter_fan_control = false;
-            supp_inter_fan_speed = 0;
-            ext_peri_fan_control = false;
-            ext_peri_fan_speed = 0;
-            fan_speed_new      = 0;
+            fan_control[0] = true;
+            fan_speeds[0] = 0;
+            for (int i = 1; i < ExtrusionRole::erCount; i++) {
+                fan_control[i] = false;
+                fan_speeds[i] = 0;
+            }
         }
-        if (fan_speed_new != m_fan_speed) {
-            m_fan_speed = fan_speed_new;
+        if (fan_speeds[0] != m_fan_speed) {
+            m_fan_speed = fan_speeds[0];
             new_gcode  += GCodeWriter::set_fan(m_config.gcode_flavor, m_config.gcode_comments, m_fan_speed, EXTRUDER_CONFIG(extruder_fan_offset), m_config.fan_percentage);
         }
     };
     //set to know all fan modifiers that can be applied ( TYPE_BRIDGE_FAN_END, TYPE_TOP_FAN_START, TYPE_SUPP_INTER_FAN_START, TYPE_EXTERNAL_PERIMETER).
-    std::unordered_set<CoolingLine::Type> current_fan_sections;
+    std::vector<ExtrusionRole> extrude_tree;
     const char         *pos               = gcode.c_str();
     int                 current_feedrate  = 0;
     int                 stored_fan_speed = m_fan_speed;
@@ -965,57 +981,15 @@ std::string CoolingBuffer::apply_layer_cooldown(
             stored_fan_speed = m_fan_speed;
         } else if (line->type & CoolingLine::TYPE_RESTORE_AFTER_WT) {
             new_gcode += GCodeWriter::set_fan(m_config.gcode_flavor, m_config.gcode_comments, stored_fan_speed, EXTRUDER_CONFIG(extruder_fan_offset), m_config.fan_percentage);
-        } else if (line->type & CoolingLine::TYPE_BRIDGE_FAN_START) {
-            if (bridge_fan_control && current_fan_sections.find(CoolingLine::TYPE_BRIDGE_FAN_START) == current_fan_sections.end()) {
-                fan_need_set = true;
-                current_fan_sections.insert(CoolingLine::TYPE_BRIDGE_FAN_START);
-            }
-        } else if (line->type & CoolingLine::TYPE_BRIDGE_FAN_END) {
-            if (bridge_fan_control || current_fan_sections.find(CoolingLine::TYPE_BRIDGE_FAN_START) != current_fan_sections.end()) {
-                fan_need_set = true;
-                current_fan_sections.erase(CoolingLine::TYPE_BRIDGE_FAN_START);
-            }
-        } else if (line->type & CoolingLine::TYPE_BRIDGE_INTERNAL_FAN_START) {
-            if (bridge_internal_fan_control && current_fan_sections.find(CoolingLine::TYPE_BRIDGE_INTERNAL_FAN_START) == current_fan_sections.end()) {
-                fan_need_set = true;
-                current_fan_sections.insert(CoolingLine::TYPE_BRIDGE_INTERNAL_FAN_START);
-            }
-        } else if (line->type & CoolingLine::TYPE_BRIDGE_INTERNAL_FAN_END) {
-            if (bridge_internal_fan_control || current_fan_sections.find(CoolingLine::TYPE_BRIDGE_INTERNAL_FAN_START) != current_fan_sections.end()) {
-                fan_need_set = true;
-                current_fan_sections.erase(CoolingLine::TYPE_BRIDGE_INTERNAL_FAN_START);
-            }
-        } else if (line->type & CoolingLine::TYPE_TOP_FAN_START) {
-            if (top_fan_control && current_fan_sections.find(CoolingLine::TYPE_TOP_FAN_START) == current_fan_sections.end()) {
-                fan_need_set = true;
-                current_fan_sections.insert(CoolingLine::TYPE_TOP_FAN_START);
-            }
-        } else if (line->type & CoolingLine::TYPE_TOP_FAN_END) {
-            if (top_fan_control || current_fan_sections.find(CoolingLine::TYPE_TOP_FAN_START) != current_fan_sections.end()) {
-                fan_need_set = true;
-                current_fan_sections.erase(CoolingLine::TYPE_TOP_FAN_START);
-            }
-        } else if (line->type & CoolingLine::TYPE_SUPP_INTER_FAN_START) {
-            if (supp_inter_fan_control && current_fan_sections.find(CoolingLine::TYPE_SUPP_INTER_FAN_START) == current_fan_sections.end()) {
-                fan_need_set = true;
-                current_fan_sections.insert(CoolingLine::TYPE_SUPP_INTER_FAN_START);
-            }
-        } else if (line->type & CoolingLine::TYPE_SUPP_INTER_FAN_END) {
-            if (supp_inter_fan_control || current_fan_sections.find(CoolingLine::TYPE_SUPP_INTER_FAN_START) != current_fan_sections.end()) {
-                fan_need_set = true;
-                current_fan_sections.erase(CoolingLine::TYPE_SUPP_INTER_FAN_START);
-            }
+        } else if (line->type & CoolingLine::TYPE_EXTRUDE_START) {
+            assert(CoolingLine::to_extrusion_role(uint32_t(line->type)) != 0);
+            extrude_tree.push_back(CoolingLine::to_extrusion_role(uint32_t(line->type)));
+            fan_need_set = true;
         } else if (line->type & CoolingLine::TYPE_EXTRUDE_END) {
-            if (ext_peri_fan_control || current_fan_sections.find(CoolingLine::TYPE_EXTERNAL_PERIMETER) != current_fan_sections.end()) {
-                fan_need_set = true;
-                current_fan_sections.erase(CoolingLine::TYPE_EXTERNAL_PERIMETER);
-            }
-        } else if (line->type & (CoolingLine::TYPE_ADJUSTABLE | CoolingLine::TYPE_ADJUSTABLE_EMPTY | CoolingLine::TYPE_EXTERNAL_PERIMETER | CoolingLine::TYPE_WIPE | CoolingLine::TYPE_HAS_F)) {
-            //ext_peri_fan_speed
-            if ((line->type & CoolingLine::TYPE_EXTERNAL_PERIMETER) != 0 && ext_peri_fan_control && current_fan_sections.find(CoolingLine::TYPE_EXTERNAL_PERIMETER) == current_fan_sections.end()) {
-                fan_need_set = true;
-                current_fan_sections.insert(CoolingLine::TYPE_EXTERNAL_PERIMETER);
-            }
+            assert(extrude_tree.size() > 0);
+            extrude_tree.pop_back();
+            fan_need_set = true;
+        } else if (line->type & (CoolingLine::TYPE_ADJUSTABLE | CoolingLine::TYPE_ADJUSTABLE_EMPTY | CoolingLine::TYPE_ADJUSTABLE_MAYBE | CoolingLine::TYPE_WIPE | CoolingLine::TYPE_HAS_F)) {
 
             // Find the start of a comment, or roll to the end of line.
             const char *end = line_start;
@@ -1031,7 +1005,7 @@ std::string CoolingBuffer::apply_layer_cooldown(
             new_feedrate = line->slowdown ? int(floor(60. * line->feedrate + 0.5)) : atoi(fpos);
             if (new_feedrate == current_feedrate) {
                 // No need to change the F value.
-                if ((line->type & (CoolingLine::TYPE_ADJUSTABLE | CoolingLine::TYPE_ADJUSTABLE_EMPTY | CoolingLine::TYPE_EXTERNAL_PERIMETER | CoolingLine::TYPE_WIPE)) || line->length == 0.)
+                if ((line->type & (CoolingLine::TYPE_ADJUSTABLE | CoolingLine::TYPE_ADJUSTABLE_EMPTY | CoolingLine::TYPE_ADJUSTABLE_MAYBE | CoolingLine::TYPE_WIPE)) || line->length == 0.)
                     // Feedrate does not change and this line does not move the print head. Skip the complete G-code line including the G-code comment.
                     end = line_end;
                 else
@@ -1078,12 +1052,14 @@ std::string CoolingBuffer::apply_layer_cooldown(
             }
             // Process the rest of the line.
             if (end < line_end) {
-                if (line->type & (CoolingLine::TYPE_ADJUSTABLE | CoolingLine::TYPE_ADJUSTABLE_EMPTY | CoolingLine::TYPE_EXTERNAL_PERIMETER | CoolingLine::TYPE_WIPE)) {
-                    // Process comments, remove ";_EXTRUDE_SET_SPEED", ";_EXTERNAL_PERIMETER", ";_WIPE"
+                if (line->type & (CoolingLine::TYPE_ADJUSTABLE | CoolingLine::TYPE_ADJUSTABLE_EMPTY | CoolingLine::TYPE_ADJUSTABLE_MAYBE | CoolingLine::TYPE_WIPE)) {
+                    // Process comments, remove ";_EXTRUDE_SET_SPEED", ";_EXTRUDE_SET_SPEED_MAYBE", ";_WIPE"
                     std::string comment(end, line_end);
-                    boost::replace_all(comment, ";_EXTRUDE_SET_SPEED", "");
-                    if (line->type & CoolingLine::TYPE_EXTERNAL_PERIMETER)
-                        boost::replace_all(comment, ";_EXTERNAL_PERIMETER", "");
+                    if (line->type & (CoolingLine::TYPE_ADJUSTABLE_MAYBE)) {
+                        boost::replace_all(comment, ";_EXTRUDE_SET_SPEED_MAYBE", "");
+                    } else {
+                        boost::replace_all(comment, ";_EXTRUDE_SET_SPEED", "");
+                    }
                     if (line->type & CoolingLine::TYPE_WIPE)
                         boost::replace_all(comment, ";_WIPE", "");
                     new_gcode += comment;
@@ -1096,19 +1072,19 @@ std::string CoolingBuffer::apply_layer_cooldown(
             new_gcode.append(line_start, line_end - line_start);
         }
         if (fan_need_set) {
-            //choose the speed with highest priority
-            if (current_fan_sections.find(CoolingLine::TYPE_BRIDGE_FAN_START) != current_fan_sections.end())
-                new_gcode  += GCodeWriter::set_fan(m_config.gcode_flavor, m_config.gcode_comments, bridge_fan_speed, EXTRUDER_CONFIG(extruder_fan_offset), m_config.fan_percentage);
-            else if (current_fan_sections.find(CoolingLine::TYPE_BRIDGE_INTERNAL_FAN_START) != current_fan_sections.end())
-                new_gcode  += GCodeWriter::set_fan(m_config.gcode_flavor, m_config.gcode_comments, bridge_internal_fan_speed, EXTRUDER_CONFIG(extruder_fan_offset), m_config.fan_percentage);
-            else if (current_fan_sections.find(CoolingLine::TYPE_TOP_FAN_START) != current_fan_sections.end())
-                new_gcode  += GCodeWriter::set_fan(m_config.gcode_flavor, m_config.gcode_comments, top_fan_speed, EXTRUDER_CONFIG(extruder_fan_offset), m_config.fan_percentage);
-            else if (current_fan_sections.find(CoolingLine::TYPE_SUPP_INTER_FAN_START) != current_fan_sections.end())
-                new_gcode  += GCodeWriter::set_fan(m_config.gcode_flavor, m_config.gcode_comments, supp_inter_fan_speed, EXTRUDER_CONFIG(extruder_fan_offset), m_config.fan_percentage);
-            else if (current_fan_sections.find(CoolingLine::TYPE_EXTERNAL_PERIMETER) != current_fan_sections.end())
-                new_gcode  += GCodeWriter::set_fan(m_config.gcode_flavor, m_config.gcode_comments, ext_peri_fan_speed, EXTRUDER_CONFIG(extruder_fan_offset), m_config.fan_percentage);
-            else
-                new_gcode  += GCodeWriter::set_fan(m_config.gcode_flavor, m_config.gcode_comments, m_fan_speed, EXTRUDER_CONFIG(extruder_fan_offset), m_config.fan_percentage);
+            //use the most current fan
+            bool fan_set = false;
+            for (size_t i = extrude_tree.size() - 1; i < extrude_tree.size(); --i) {
+                if (fan_control[extrude_tree[i]]) {
+                    new_gcode += GCodeWriter::set_fan(m_config.gcode_flavor, m_config.gcode_comments, fan_speeds[extrude_tree[i]], EXTRUDER_CONFIG(extruder_fan_offset), m_config.fan_percentage);
+                    fan_set = true;
+                    break;
+                }
+            }
+            if (!fan_set) {
+                //return to default
+                new_gcode += GCodeWriter::set_fan(m_config.gcode_flavor, m_config.gcode_comments, m_fan_speed, EXTRUDER_CONFIG(extruder_fan_offset), m_config.fan_percentage);
+            }
             fan_need_set = false;
         }
         pos = line_end;
diff --git a/src/libslic3r/GCode/FanMover.cpp b/src/libslic3r/GCode/FanMover.cpp
index 434a80cf61e..159d13c293e 100644
--- a/src/libslic3r/GCode/FanMover.cpp
+++ b/src/libslic3r/GCode/FanMover.cpp
@@ -308,7 +308,7 @@ void FanMover::_process_gcode_line(GCodeReader& reader, const GCodeReader::GCode
                                 }
 
                                 //if kickstart
-                                // first erase everything lower that that value
+                                // first erase everything lower than that value
                                 _remove_slow_fan(fan_speed, m_buffer_time_size + 1);
                                 // then erase everything lower that kickstart
                                 _remove_slow_fan(fan_baseline, kickstart);
@@ -341,7 +341,7 @@ void FanMover::_process_gcode_line(GCodeReader& reader, const GCodeReader::GCode
                                 }
                                 m_front_buffer_fan_speed = fan_speed;
                             } else {
-                                // first erase everything lower that that value
+                                // first erase everything lower than that value
                                 _remove_slow_fan(fan_speed, m_buffer_time_size + 1);
                                 // then write the fan command
                                 if (!m_buffer.empty() && (m_buffer_time_size - m_buffer.front().time * 0.1) > nb_seconds_delay) {
diff --git a/src/libslic3r/GCode/WipeTower.cpp b/src/libslic3r/GCode/WipeTower.cpp
index 76d7d142678..4df3e377d96 100644
--- a/src/libslic3r/GCode/WipeTower.cpp
+++ b/src/libslic3r/GCode/WipeTower.cpp
@@ -507,10 +507,11 @@ class WipeTowerWriter
 
     WipeTowerWriter& set_fan(unsigned speed, const std::string &comment)
 	{
+        assert(comment.empty() || comment[0] == ';' || (comment.size() > 1 && comment[0] == ' ' && comment[1] == ';'));
 		if (speed == m_last_fan_speed)
 			return *this;
 		if (speed == 0)
-			m_gcode += "M107\n";
+			m_gcode += "M107" + comment + "\n";
 		else
             m_gcode += "M106 S" + std::to_string(unsigned(255.0 * speed / 100.0)) + comment + "\n";
 		m_last_fan_speed = speed;
diff --git a/src/libslic3r/Preset.cpp b/src/libslic3r/Preset.cpp
index fc79a051ff7..60c4ab3e0d3 100644
--- a/src/libslic3r/Preset.cpp
+++ b/src/libslic3r/Preset.cpp
@@ -745,21 +745,29 @@ static std::vector<std::string> s_Preset_filament_options {
         "filament_dip_insertion_speed",
         "filament_dip_extraction_speed",  //skinnydip params end
         "temperature", "first_layer_temperature", "bed_temperature", "first_layer_bed_temperature", 
-        "full_fan_speed_layer",
+        // cooling
         "fan_always_on", 
         "min_fan_speed",
         "max_fan_speed", 
         "bridge_fan_speed",
         "bridge_internal_fan_speed",
+        "external_perimeter_fan_speed",
+        "gap_fill_fan_speed",
+        "infill_fan_speed",
+        "overhangs_fan_speed",
+        "perimeter_fan_speed",
+        "solid_infill_fan_speed",
+        "support_material_fan_speed",
         "support_material_interface_fan_speed",
         "top_fan_speed",
         "disable_fan_first_layers",
-        "fan_below_layer_time", 
+        "full_fan_speed_layer",
+        "fan_below_layer_time",
         "slowdown_below_layer_time",
         "max_speed_reduction",
         "min_print_speed",
+        // custom gcode
         "start_filament_gcode", "end_filament_gcode",
-        "external_perimeter_fan_speed",
         // Retract overrides
         "filament_retract_length", "filament_retract_lift", "filament_retract_lift_above", "filament_retract_lift_below", 
         "filament_retract_speed", "filament_deretract_speed", "filament_retract_restart_extra", 
diff --git a/src/libslic3r/Print.cpp b/src/libslic3r/Print.cpp
index 9f347976001..ecf364e8b8b 100644
--- a/src/libslic3r/Print.cpp
+++ b/src/libslic3r/Print.cpp
@@ -117,6 +117,7 @@ bool Print::invalidate_state_by_config_options(const ConfigOptionResolver& /* ne
         "first_layer_min_speed",
         "full_fan_speed_layer",
         "gap_fill_acceleration",
+        "gap_fill_fan_speed",
         "gap_fill_flow_match_perimeter",
         "gap_fill_speed",
         "gcode_comments",
@@ -125,6 +126,7 @@ bool Print::invalidate_state_by_config_options(const ConfigOptionResolver& /* ne
         "gcode_precision_xyz",
         "gcode_precision_e",
         "infill_acceleration",
+        "infill_fan_speed",
         "ironing_acceleration",
         "layer_gcode",
         "max_fan_speed",
@@ -146,9 +148,11 @@ bool Print::invalidate_state_by_config_options(const ConfigOptionResolver& /* ne
         "only_retract_when_crossing_perimeters",
         "output_filename_format",
         "overhangs_acceleration",
+        "overhangs_fan_speed",
         "perimeter_acceleration",
         "post_process",
         "gcode_substitutions",
+        "perimeter_fan_speed",
         "printer_notes",
         "retract_before_travel",
         "retract_before_wipe",
@@ -167,7 +171,9 @@ bool Print::invalidate_state_by_config_options(const ConfigOptionResolver& /* ne
         "single_extruder_multi_material_priming",
         "slowdown_below_layer_time",
         "solid_infill_acceleration",
+        "solid_infill_fan_speed",
         "support_material_acceleration",
+        "support_material_fan_speed",
         "support_material_interface_acceleration",
         "support_material_interface_fan_speed",
         "standby_temperature_delta",
diff --git a/src/libslic3r/PrintConfig.cpp b/src/libslic3r/PrintConfig.cpp
index a92d62c566d..fdb04d64eab 100644
--- a/src/libslic3r/PrintConfig.cpp
+++ b/src/libslic3r/PrintConfig.cpp
@@ -729,8 +729,8 @@ void PrintConfigDef::init_fff_params()
     def->label = L("Bridges fan speed");
     def->category = OptionCategory::cooling;
     def->tooltip = L("This fan speed is enforced during bridges and overhangs. It won't slow down the fan if it's currently running at a higher speed."
-        "\nSet to -1 to disable this override."
-        "\nCan only be overriden by disable_fan_first_layers.");
+        "\nSet to -1 to disable this override (Bridge will use default fan speed)."
+        "\nCan be disabled by disable_fan_first_layers and increased by low layer time.");
     def->sidetext = L("%");
     def->min = -1;
     def->max = 100;
@@ -744,7 +744,7 @@ void PrintConfigDef::init_fff_params()
     def->tooltip = L("This fan speed is enforced during all infill bridges. It won't slow down the fan if it's currently running at a higher speed."
         "\nSet to 1 to follow default speed."
         "\nSet to -1 to disable this override (internal bridges will use Bridges fan speed)."
-        "\nCan only be overriden by disable_fan_first_layers.");
+        "\nCan be disabled by disable_fan_first_layers and increased by low layer time.");
     def->sidetext = L("%");
     def->min = -1;
     def->max = 100;
@@ -1521,11 +1521,12 @@ void PrintConfigDef::init_fff_params()
 
     def = this->add("external_perimeter_fan_speed", coInts);
     def->label = L("External perimeter fan speed");
-    def->tooltip = L("When set to a non-zero value this fan speed is used only for external perimeters (visible ones). "
+    def->tooltip = L("When set to a non-zero value this fan speed is used only for external perimeters (visible ones) and thin walls."
                     "\nSet to 1 to disable the fan."
                     "\nSet to -1 to use the normal fan speed on external perimeters."
                     "External perimeters can benefit from higher fan speed to improve surface finish, "
-                    "while internal perimeters, infill, etc. benefit from lower fan speed to improve layer adhesion.");
+                    "while internal perimeters, infill, etc. benefit from lower fan speed to improve layer adhesion."
+                    "\nCan be disabled by disable_fan_first_layers, slowed down by full_fan_speed_layer and increased by low layer time.");
     def->sidetext = L("%");
     def->min = -1;
     def->max = 100;
@@ -2586,8 +2587,9 @@ void PrintConfigDef::init_fff_params()
     def->category = OptionCategory::filament;
     def->tooltip = L("Fan speed will be ramped up linearly from zero at layer \"disable_fan_first_layers\" "
                    "to maximum at layer \"full_fan_speed_layer\". "
-                   "\"full_fan_speed_layer\" will be ignored if lower than \"disable_fan_first_layers\", in which case "
-                   "the fan will be running at maximum allowed speed at layer \"disable_fan_first_layers\" + 1.");
+                   "\"full_fan_speed_layer\" will be ignored if equal or lower than \"disable_fan_first_layers\", in which case "
+                   "the fan will be running at maximum allowed speed at layer \"disable_fan_first_layers\" + 1."
+                   "\nset 0 to disable");
     def->min = 0;
     def->max = 1000;
     def->mode = comExpert | comPrusa;
@@ -2672,6 +2674,20 @@ void PrintConfigDef::init_fff_params()
     def->mode = comExpert | comSuSi;
     def->set_default_value(new ConfigOptionFloatOrPercent{ 0, false });
 
+    def = this->add("gap_fill_fan_speed", coInts);
+    def->label = L("Gap Fill fan speed");
+    def->category = OptionCategory::cooling;
+    def->tooltip = L("This fan speed is enforced during all gap fill Perimeter moves"
+        "\nSet to 1 to disable fan."
+        "\nSet to -1 to disable this override (Gap Fill will use default fan speed)."
+        "\nCan be disabled by disable_fan_first_layers, slowed down by full_fan_speed_layer and increased by low layer time.");
+    def->sidetext = L("%");
+    def->min = -1;
+    def->max = 100;
+    def->mode = comAdvancedE | comSuSi;
+    def->is_vector_extruder = true;
+    def->set_default_value(new ConfigOptionInts{ -1 });
+
     def = this->add("gap_fill_flow_match_perimeter", coPercent);
     def->label = L("Cap with perimeter flow");
     def->full_label = L("Gapfill: cap speed with perimeter flow");
@@ -3107,6 +3123,20 @@ void PrintConfigDef::init_fff_params()
     def->mode = comAdvancedE | comSuSi;
     def->set_default_value(new ConfigOptionFloatOrPercent(100, true, false));
 
+    def = this->add("infill_fan_speed", coInts);
+    def->label = L("Internal Infill fan speed");
+    def->category = OptionCategory::cooling;
+    def->tooltip = L("This fan speed is enforced during all Internal Infill moves"
+        "\nSet to 1 to disable fan."
+        "\nSet to -1 to disable this override (Internal Infill will use default fan speed)."
+        "\nCan be disabled by disable_fan_first_layers, slowed down by full_fan_speed_layer and increased by low layer time.");
+    def->sidetext = L("%");
+    def->min = -1;
+    def->max = 100;
+    def->mode = comAdvancedE | comSuSi;
+    def->is_vector_extruder = true;
+    def->set_default_value(new ConfigOptionInts{ -1 });
+
     def = this->add("infill_first", coBool);
     def->label = L("Infill before perimeters");
     def->category = OptionCategory::infill;
@@ -3848,6 +3878,20 @@ void PrintConfigDef::init_fff_params()
     def->mode = comExpert | comSuSi;
     def->set_default_value(new ConfigOptionFloatOrPercent(0,false));
 
+    def = this->add("overhangs_fan_speed", coInts);
+    def->label = L("Overhang Perimeter fan speed");
+    def->category = OptionCategory::cooling;
+    def->tooltip = L("This fan speed is enforced during all Overhang Perimeter moves"
+        "\nSet to 1 to disable fan."
+        "\nSet to -1 to disable this override (Overhang Perimeter use default fan speed)."
+        "\nCan be disabled by disable_fan_first_layers and increased by low layer time.");
+    def->sidetext = L("%");
+    def->min = -1;
+    def->max = 100;
+    def->mode = comAdvancedE | comSuSi;
+    def->is_vector_extruder = true;
+    def->set_default_value(new ConfigOptionInts{ -1 });
+
     def = this->add("overhangs_speed", coFloatOrPercent);
     def->label = L("Overhangs");
     def->full_label = L("Overhangs speed");
@@ -4053,6 +4097,20 @@ void PrintConfigDef::init_fff_params()
     def->mode = comExpert | comSuSi;
     def->set_default_value(new ConfigOptionFloatOrPercent(false, 0));
 
+    def = this->add("perimeter_fan_speed", coInts);
+    def->label = L("Internal Perimeter fan speed");
+    def->category = OptionCategory::cooling;
+    def->tooltip = L("This fan speed is enforced during all Perimeter moves"
+        "\nSet to 1 to disable fan."
+        "\nSet to -1 to disable this override (Internal Perimeter use default fan speed)."
+        "\nCan be disabled by disable_fan_first_layers, slowed down by full_fan_speed_layer and increased by low layer time.");
+    def->sidetext = L("%");
+    def->min = -1;
+    def->max = 100;
+    def->mode = comAdvancedE | comSuSi;
+    def->is_vector_extruder = true;
+    def->set_default_value(new ConfigOptionInts{ -1 });
+
     def = this->add("perimeter_loop", coBool);
     def->label = L("Perimeters loop");
     def->full_label = L("Perimeters loop");
@@ -4870,6 +4928,20 @@ void PrintConfigDef::init_fff_params()
     def->mode = comAdvancedE | comSuSi;
     def->set_default_value(new ConfigOptionFloatOrPercent(100, true, false));
 
+    def = this->add("solid_infill_fan_speed", coInts);
+    def->label = L("Solid Infill fan speed");
+    def->category = OptionCategory::cooling;
+    def->tooltip = L("This fan speed is enforced during all Solid Infill moves"
+        "\nSet to 1 to disable fan."
+        "\nSet to -1 to disable this override (Solid Infill will use default fan speed)."
+        "\nCan be disabled by disable_fan_first_layers, slowed down by full_fan_speed_layer and increased by low layer time.");
+    def->sidetext = L("%");
+    def->min = -1;
+    def->max = 100;
+    def->mode = comAdvancedE | comSuSi;
+    def->is_vector_extruder = true;
+    def->set_default_value(new ConfigOptionInts{ -1 });
+
     def = this->add("solid_infill_speed", coFloatOrPercent);
     def->label = L("Solid");
     def->full_label = L("Solid infill speed");
@@ -5233,6 +5305,20 @@ void PrintConfigDef::init_fff_params()
     def->mode = comAdvancedE | comPrusa;
     def->set_default_value(new ConfigOptionFloatOrPercent(0, false));
 
+    def = this->add("support_material_fan_speed", coInts);
+    def->label = L("Support Material fan speed");
+    def->category = OptionCategory::cooling;
+    def->tooltip = L("This fan speed is enforced during all support moves"
+        "\nSet to 0 to disable fan."
+        "\nSet to -1 to disable this override (Support will use default fan speed)."
+        "\nCan be disabled by disable_fan_first_layers, slowed down by full_fan_speed_layer.");
+    def->sidetext = L("%");
+    def->min = -1;
+    def->max = 100;
+    def->mode = comAdvancedE | comSuSi;
+    def->is_vector_extruder = true;
+    def->set_default_value(new ConfigOptionInts{ -1 });
+
     def = this->add("support_material_interface_angle", coFloat);
     def->label = L("Pattern angle");
     def->full_label = L("Support interface pattern angle");
@@ -5258,8 +5344,8 @@ void PrintConfigDef::init_fff_params()
     def->label = L("Support interface fan speed");
     def->category = OptionCategory::cooling;
     def->tooltip = L("This fan speed is enforced during all support interfaces, to be able to weaken their bonding with a high fan speed."
-        "\nSet to 1 to disable the fan."
-        "\nSet to -1 to disable this override."
+        "\nSet to 0 to disable the fan."
+        "\nSet to -1 to disable this override (Support Interface will use Support)."
         "\nCan only be overriden by disable_fan_first_layers.");
     def->sidetext = L("%");
     def->min = -1;
@@ -5678,12 +5764,12 @@ void PrintConfigDef::init_fff_params()
     def->set_default_value(new ConfigOptionStrings(""));
 
     def = this->add("top_fan_speed", coInts);
-    def->label = L("Top fan speed");
+    def->label = L("Top Solid fan speed");
     def->category = OptionCategory::cooling;
-    def->tooltip = L("This fan speed is enforced during all top fills."
+    def->tooltip = L("This fan speed is enforced during all top fills (including ironing)."
         "\nSet to 1 to disable the fan."
-        "\nSet to -1 to disable this override."
-        "\nCan only be overriden by disable_fan_first_layers.");
+        "\nSet to -1 to disable this override (Top Solid Infill will use Solid Infill)."
+        "\nCan be disabled by disable_fan_first_layers, slowed down by full_fan_speed_layer.");
     def->sidetext = L("%");
     def->min = -1;
     def->max = 100;
@@ -7700,6 +7786,7 @@ std::unordered_set<std::string> prusa_export_to_remove_keys = {
 "first_layer_size_compensation_layers",
 "gap_fill_acceleration",
 "gap_fill_extension",
+"gap_fill_fan_speed",
 "gap_fill_flow_match_perimeter",
 "gap_fill_last",
 "gap_fill_infill",
@@ -7719,6 +7806,7 @@ std::unordered_set<std::string> prusa_export_to_remove_keys = {
 "infill_dense_algo",
 "infill_dense",
 "infill_extrusion_spacing",
+"infill_fan_speed",
 "ironing_acceleration",
 "lift_min",
 "machine_max_acceleration_travel",
@@ -7743,6 +7831,7 @@ std::unordered_set<std::string> prusa_export_to_remove_keys = {
 "only_one_perimeter_first_layer",
 "over_bridge_flow_ratio",
 "overhangs_acceleration",
+"overhangs_fan_speed",
 "overhangs_reverse_threshold",
 "overhangs_reverse",
 "overhangs_speed",
@@ -7750,6 +7839,7 @@ std::unordered_set<std::string> prusa_export_to_remove_keys = {
 "overhangs_width_speed",
 "perimeter_bonding",
 "perimeter_extrusion_spacing",
+"perimeter_fan_speed",
 "perimeter_loop_seam",
 "perimeter_loop",
 "perimeter_overlap",
@@ -7783,10 +7873,12 @@ std::unordered_set<std::string> prusa_export_to_remove_keys = {
 "solid_fill_pattern",
 "solid_infill_acceleration",
 "solid_infill_extrusion_spacing",
+"solid_infill_fan_speed",
 "start_gcode_manual",
 "support_material_angle_height",
 "support_material_acceleration",
 "support_material_contact_distance_type",
+"support_material_fan_speed",
 "support_material_interface_acceleration",
 "support_material_interface_angle",
 "support_material_interface_angle_increment",
diff --git a/src/libslic3r/PrintConfig.hpp b/src/libslic3r/PrintConfig.hpp
index 69993cd2ac0..24949305e2c 100644
--- a/src/libslic3r/PrintConfig.hpp
+++ b/src/libslic3r/PrintConfig.hpp
@@ -1170,7 +1170,9 @@ PRINT_CONFIG_CLASS_DERIVED_DEFINE(
     ((ConfigOptionInts,                 first_layer_temperature))
     ((ConfigOptionInts,                 full_fan_speed_layer))
     ((ConfigOptionFloatOrPercent,       gap_fill_acceleration))
+    ((ConfigOptionInts,                 gap_fill_fan_speed))
     ((ConfigOptionFloatOrPercent,       infill_acceleration))
+    ((ConfigOptionInts,                 infill_fan_speed))
     ((ConfigOptionFloatOrPercent,       ironing_acceleration))
     ((ConfigOptionFloat,                lift_min))
     ((ConfigOptionInts,                 max_fan_speed))
@@ -1192,7 +1194,9 @@ PRINT_CONFIG_CLASS_DERIVED_DEFINE(
     ((ConfigOptionBool,                 ooze_prevention))
     ((ConfigOptionString,               output_filename_format))
     ((ConfigOptionFloatOrPercent,       overhangs_acceleration))
+    ((ConfigOptionInts,                 overhangs_fan_speed))
     ((ConfigOptionFloatOrPercent,       perimeter_acceleration))
+    ((ConfigOptionInts,                 perimeter_fan_speed))
     ((ConfigOptionStrings,              post_process))
     ((ConfigOptionString,               print_custom_variables))
     ((ConfigOptionString,               printer_custom_variables))
@@ -1214,8 +1218,10 @@ PRINT_CONFIG_CLASS_DERIVED_DEFINE(
     ((ConfigOptionFloats,               slowdown_below_layer_time))
     ((ConfigOptionBool,                 spiral_vase))
     ((ConfigOptionFloatOrPercent,       solid_infill_acceleration))
+    ((ConfigOptionInts,                 solid_infill_fan_speed))
     ((ConfigOptionInt,                  standby_temperature_delta))
     ((ConfigOptionFloatOrPercent,       support_material_acceleration))
+    ((ConfigOptionInts,                 support_material_fan_speed))
     ((ConfigOptionFloatOrPercent,       support_material_interface_acceleration))
     ((ConfigOptionInts,                 support_material_interface_fan_speed))
     ((ConfigOptionInts,                 temperature))