diff --git a/xs/src/libslic3r/ExtrusionEntity.hpp b/xs/src/libslic3r/ExtrusionEntity.hpp
index 7eefdcdb3..d478ce659 100644
--- a/xs/src/libslic3r/ExtrusionEntity.hpp
+++ b/xs/src/libslic3r/ExtrusionEntity.hpp
@@ -303,6 +303,18 @@ inline void extrusion_entities_append_paths(ExtrusionEntitiesPtr &dst, Polylines
     polylines.clear();
 }
 
+inline void extrusion_entities_append_loops(ExtrusionEntitiesPtr &dst, Polygons &loops, ExtrusionRole role, double mm3_per_mm, float width, float height) {
+    dst.reserve(dst.size() + loops.size());
+    for (Polygon &poly : loops) {
+        if (poly.is_valid()) {
+            ExtrusionPath path(role, mm3_per_mm, width, height);
+            path.polyline.points = poly.points;
+            path.polyline.points.push_back(path.polyline.points.front());
+            dst.emplace_back(new ExtrusionLoop(std::move(path)));
+        }
+    }
+}
+
 inline void extrusion_entities_append_loops(ExtrusionEntitiesPtr &dst, Polygons &&loops, ExtrusionRole role, double mm3_per_mm, float width, float height)
 {
     dst.reserve(dst.size() + loops.size());
diff --git a/xs/src/libslic3r/Fill/FillBase.cpp b/xs/src/libslic3r/Fill/FillBase.cpp
index e1eae0244..7fa0cb215 100644
--- a/xs/src/libslic3r/Fill/FillBase.cpp
+++ b/xs/src/libslic3r/Fill/FillBase.cpp
@@ -22,6 +22,7 @@ Fill* Fill::new_from_type(const InfillPattern type)
 {
     switch (type) {
     case ipConcentric:          return new FillConcentric();
+    case ipConcentricGapFill:   return new FillConcentricWGapFill();
     case ipHoneycomb:           return new FillHoneycomb();
     case ip3DHoneycomb:         return new Fill3DHoneycomb();
     case ipGyroid:              return new FillGyroid();
diff --git a/xs/src/libslic3r/Fill/FillConcentric.cpp b/xs/src/libslic3r/Fill/FillConcentric.cpp
index b21ad2799..c6e362ff6 100644
--- a/xs/src/libslic3r/Fill/FillConcentric.cpp
+++ b/xs/src/libslic3r/Fill/FillConcentric.cpp
@@ -1,10 +1,13 @@
 #include "../ClipperUtils.hpp"
 #include "../ExPolygon.hpp"
 #include "../Surface.hpp"
+#include "../ExtrusionEntityCollection.hpp"
+#include "../MedialAxis.hpp"
 
 #include "FillConcentric.hpp"
 
 namespace Slic3r {
+    
 
 void FillConcentric::_fill_surface_single(
     const FillParams                &params, 
@@ -61,4 +64,98 @@ void FillConcentric::_fill_surface_single(
     // We want the loops to be split inside the G-code generator to get optimum path planning.
 }
 
+void FillConcentricWGapFill::fill_surface_extrusion(const Surface *surface, const FillParams &params,
+    const Flow &flow, const ExtrusionRole &role, ExtrusionEntitiesPtr &out) {
+
+    // Perform offset.
+    Slic3r::ExPolygons expp = offset_ex(surface->expolygon, float(scale_(0 - 0.5 * this->spacing)));
+    // Create the infills for each of the regions.
+    Polylines polylines_out;
+    for (size_t i = 0; i < expp.size(); ++i) {
+        //_fill_surface_single(
+        //params,
+        //surface->thickness_layers,
+        //_infill_direction(surface),
+        //expp[i],
+        //polylines_out);
+        ExPolygon expolygon = expp[i];
+
+        coordf_t init_spacing = this->spacing;
+
+        // no rotation is supported for this infill pattern
+        BoundingBox bounding_box = expolygon.contour.bounding_box();
+
+        coord_t min_spacing = scale_(this->spacing);
+        coord_t distance = coord_t(min_spacing / params.density);
+
+        if (params.density > 0.9999f && !params.dont_adjust) {
+            distance = this->_adjust_solid_spacing(bounding_box.size().x, distance);
+            this->spacing = unscale(distance);
+        }
+
+        ExPolygons gaps;
+        Polygons loops = (Polygons)expolygon;
+        Polygons last = loops;
+        while (!last.empty()) {
+            Polygons next_onion = offset2(last, -(distance + min_spacing / 2), +min_spacing / 2);
+            loops.insert(loops.end(), next_onion.begin(), next_onion.end());
+            append(gaps, diff_ex(
+                offset(last, -0.5f * distance),
+                offset(next_onion, 0.5f * distance + 10)));  // safety offset
+            last = next_onion;
+        }
+
+        // generate paths from the outermost to the innermost, to avoid
+        // adhesion problems of the first central tiny loops
+        //note: useless if we don't apply no_sort flag
+        //loops = union_pt_chained(loops, false);
+
+
+        //get the role
+        ExtrusionRole good_role = role;
+        if (good_role == erNone || good_role == erCustom) {
+            good_role = (flow.bridge ? erBridgeInfill :
+                (surface->is_solid() ?
+                ((surface->is_top()) ? erTopSolidInfill : erSolidInfill) :
+                erInternalInfill));
+        }
+
+        ExtrusionEntityCollection *coll_nosort = new ExtrusionEntityCollection();
+        coll_nosort->no_sort = true; //can be sorted inside the pass
+        extrusion_entities_append_loops(
+            coll_nosort->entities, loops,
+            good_role,
+            flow.mm3_per_mm() * params.flow_mult,
+            flow.width * params.flow_mult,
+            flow.height);
+
+        //add gapfills
+        if (!gaps.empty() && params.density >= 1) {
+            // collapse 
+            double min = 0.2 * distance * (1 - INSET_OVERLAP_TOLERANCE);
+            double max = 2. * distance;
+            ExPolygons gaps_ex = diff_ex(
+                offset2_ex(gaps, -min / 2, +min / 2),
+                offset2_ex(gaps, -max / 2, +max / 2),
+                true);
+            ThickPolylines polylines;
+            for (const ExPolygon &ex : gaps_ex) {
+                //remove too small gaps that are too hard to fill.
+                //ie one that are smaller than an extrusion with width of min and a length of max.
+                if (ex.area() > min*max) {
+                    ex.medial_axis(ex, max, min, &polylines, flow.height);
+                }
+            }
+            if (!polylines.empty()) {
+                ExtrusionEntityCollection gap_fill = thin_variable_width(polylines, erGapFill, flow);
+                coll_nosort->append(gap_fill.entities);
+            }
+        }
+
+        if (!coll_nosort->entities.empty())
+            out.push_back(coll_nosort);
+        else delete coll_nosort;
+    }
+}
+
 } // namespace Slic3r
diff --git a/xs/src/libslic3r/Fill/FillConcentric.hpp b/xs/src/libslic3r/Fill/FillConcentric.hpp
index 1286858ea..918a370a7 100644
--- a/xs/src/libslic3r/Fill/FillConcentric.hpp
+++ b/xs/src/libslic3r/Fill/FillConcentric.hpp
@@ -12,16 +12,29 @@ public:
 
 protected:
     virtual Fill* clone() const { return new FillConcentric(*this); };
-	virtual void _fill_surface_single(
-	    const FillParams                &params, 
-	    unsigned int                     thickness_layers,
-	    const std::pair<float, Point>   &direction, 
-	    ExPolygon                       &expolygon, 
-	    Polylines                       &polylines_out);
+    virtual void _fill_surface_single(
+        const FillParams                &params,
+        unsigned int                     thickness_layers,
+        const std::pair<float, Point>   &direction,
+        ExPolygon                       &expolygon,
+        Polylines                       &polylines_out);
 
 	virtual bool no_sort() const { return true; }
 };
 
+
+class FillConcentricWGapFill : public Fill {
+public:
+    virtual ~FillConcentricWGapFill() {}
+
+protected:
+    virtual Fill* clone() const { return new FillConcentricWGapFill(*this); };
+    virtual void fill_surface_extrusion(const Surface *surface, const FillParams &params,
+        const Flow &flow, const ExtrusionRole &role, ExtrusionEntitiesPtr &out);
+
+    virtual bool no_sort() const { return true; }
+};
+
 } // namespace Slic3r
 
 #endif // slic3r_FillConcentric_hpp_
diff --git a/xs/src/libslic3r/Fill/FillSmooth.cpp b/xs/src/libslic3r/Fill/FillSmooth.cpp
index 7168c5882..3b936a653 100644
--- a/xs/src/libslic3r/Fill/FillSmooth.cpp
+++ b/xs/src/libslic3r/Fill/FillSmooth.cpp
@@ -269,8 +269,9 @@ namespace Slic3r {
             }
         }
 
-        if (!eecroot->entities.empty())
+        if (!eecroot->entities.empty()) 
             out.push_back(eecroot);
+        else delete eecroot;
 
     }
 
diff --git a/xs/src/libslic3r/MedialAxis.cpp b/xs/src/libslic3r/MedialAxis.cpp
index 7be8c0958..64bd1bdf4 100644
--- a/xs/src/libslic3r/MedialAxis.cpp
+++ b/xs/src/libslic3r/MedialAxis.cpp
@@ -301,13 +301,14 @@ remove_point_too_near(ThickPolyline* to_reduce)
             to_reduce->points.erase(to_reduce->points.begin() + id);
             to_reduce->width.erase(to_reduce->width.begin() + id);
             newdist = to_reduce->points[id].distance_to(to_reduce->points[id - 1]);
+            //if you removed a point, it check if the next one isn't too near from the previous one.
+            // if not, it bypass it.
+            if (newdist > smallest) {
+                ++id;
+            }
         }
         //go to next one
-        //if you removed a point, it check if the next one isn't too near from the previous one.
-        // if not, it byepass it.
-        if (newdist > smallest) {
-            ++id;
-        }
+        else ++id;
     }
 }
 
@@ -620,20 +621,33 @@ MedialAxis::extends_line(ThickPolyline& polyline, const ExPolygons& anchors, con
             line.a = *(polyline.points.begin() + first_idx);
         }
         // prevent the line from touching on the other side, otherwise intersection() might return that solution
-        if (polyline.points.size() == 2) line.a = line.midpoint();
+        if (polyline.points.size() == 2 && this->expolygon.contains(line.midpoint())) line.a = line.midpoint();
 
         line.extend_end(max_width);
         Point new_back;
         if (this->expolygon.contour.has_boundary_point(polyline.points.back())) {
             new_back = polyline.points.back();
         } else {
-            //TODO: verify also for holes.
-            (void)this->expolygon.contour.first_intersection(line, &new_back);
+            bool finded = this->expolygon.contour.first_intersection(line, &new_back);
+            //verify also for holes.
+            Point new_back_temp;
+            for (Polygon hole : this->expolygon.holes) {
+                if (hole.first_intersection(line, &new_back_temp)) {
+                    if (!finded || line.a.distance_to(new_back_temp) < line.a.distance_to(new_back)) {
+                        finded = true;
+                        new_back = new_back_temp;
+                    }
+                }
+            }
             // safety check if no intersection
-            if (new_back.x == 0 && new_back.y == 0) {
+            if (!finded) {
                 if (!this->expolygon.contains(line.b)) {
                     //it's outside!!!
-                    std::cout << "Error, a line is formed that start in a polygon, end outside of it can don't cross it!\n";
+                    if (!this->expolygon.contains(line.a)) {
+                        std::cout << "Error, a line is formed that start outside a polygon, end outside of it and don't cross it!\n";
+                    } else {
+                        std::cout << "Error, a line is formed that start in a polygon, end outside of it and don't cross it!\n";
+                    }
                 }
                 new_back = line.b;
             }
@@ -641,10 +655,19 @@ MedialAxis::extends_line(ThickPolyline& polyline, const ExPolygons& anchors, con
             polyline.width.push_back(polyline.width.back());
         }
         Point new_bound;
-        //TODO: verify also for holes.
-        (void)bounds.contour.first_intersection(line, &new_bound);
+        bool finded = bounds.contour.first_intersection(line, &new_bound);
+        //verify also for holes.
+        Point new_bound_temp;
+        for (Polygon hole : bounds.holes) {
+            if (hole.first_intersection(line, &new_bound_temp)) {
+                if (!finded || line.a.distance_to(new_bound_temp) < line.a.distance_to(new_bound)) {
+                    finded = true;
+                    new_bound = new_bound_temp;
+                }
+            }
+        }
         // safety check if no intersection
-        if (new_bound.x == 0 && new_bound.y == 0) {
+        if (!finded) {
             if (line.b.coincides_with_epsilon(polyline.points.back())) {
                 return;
             }
@@ -1479,4 +1502,105 @@ MedialAxis::build(ThickPolylines* polylines_out)
 
 }
 
+ExtrusionEntityCollection thin_variable_width(const ThickPolylines &polylines, ExtrusionRole role, Flow flow) {
+    // this value determines granularity of adaptive width, as G-code does not allow
+    // variable extrusion within a single move; this value shall only affect the amount
+    // of segments, and any pruning shall be performed before we apply this tolerance
+    const double tolerance = scale_(0.05);
+
+    int id_line = 0;
+    ExtrusionEntityCollection coll;
+    for (const ThickPolyline &p : polylines) {
+        id_line++;
+        ExtrusionPaths paths;
+        ExtrusionPath path(role);
+        ThickLines lines = p.thicklines();
+
+        for (int i = 0; i < (int)lines.size(); ++i) {
+            const ThickLine& line = lines[i];
+
+            const coordf_t line_len = line.length();
+            if (line_len < SCALED_EPSILON) continue;
+
+            double thickness_delta = fabs(line.a_width - line.b_width);
+            if (thickness_delta > tolerance) {
+                const unsigned short segments = ceil(thickness_delta / tolerance);
+                const coordf_t seg_len = line_len / segments;
+                Points pp;
+                std::vector<coordf_t> width;
+                {
+                    pp.push_back(line.a);
+                    width.push_back(line.a_width);
+                    for (size_t j = 1; j < segments; ++j) {
+                        pp.push_back(line.point_at(j*seg_len));
+
+                        coordf_t w = line.a_width + (j*seg_len) * (line.b_width - line.a_width) / line_len;
+                        width.push_back(w);
+                        width.push_back(w);
+                    }
+                    pp.push_back(line.b);
+                    width.push_back(line.b_width);
+
+                    assert(pp.size() == segments + 1);
+                    assert(width.size() == segments * 2);
+                }
+
+                // delete this line and insert new ones
+                lines.erase(lines.begin() + i);
+                for (size_t j = 0; j < segments; ++j) {
+                    ThickLine new_line(pp[j], pp[j + 1]);
+                    new_line.a_width = width[2 * j];
+                    new_line.b_width = width[2 * j + 1];
+                    lines.insert(lines.begin() + i + j, new_line);
+                }
+
+                --i;
+                continue;
+            }
+
+            const double w = fmax(line.a_width, line.b_width);
+            if (path.polyline.points.empty()) {
+                path.polyline.append(line.a);
+                path.polyline.append(line.b);
+                // Convert from spacing to extrusion width based on the extrusion model
+                // of a square extrusion ended with semi circles.
+                flow.width = unscale(w) + flow.height * (1. - 0.25 * PI);
+#ifdef SLIC3R_DEBUG
+                printf("  filling %f gap\n", flow.width);
+#endif
+                path.mm3_per_mm = flow.mm3_per_mm();
+                path.width = flow.width;
+                path.height = flow.height;
+            } else {
+                thickness_delta = fabs(scale_(flow.width) - w);
+                if (thickness_delta <= tolerance / 2) {
+                    // the width difference between this line and the current flow width is 
+                    // within the accepted tolerance
+                    path.polyline.append(line.b);
+                } else {
+                    // we need to initialize a new line
+                    paths.emplace_back(std::move(path));
+                    path = ExtrusionPath(role);
+                    --i;
+                }
+            }
+        }
+        if (path.polyline.is_valid())
+            paths.emplace_back(std::move(path));
+        // Append paths to collection.
+        if (!paths.empty()) {
+            if (paths.front().first_point().coincides_with(paths.back().last_point())) {
+                coll.append(ExtrusionLoop(paths));
+            } else {
+                //not a loop : avoid to "sort" it.
+                ExtrusionEntityCollection unsortable_coll(paths);
+                unsortable_coll.no_sort = true;
+                coll.append(unsortable_coll);
+            }
+        }
+    }
+
+    return coll;
+}
+
 } // namespace Slic3r
diff --git a/xs/src/libslic3r/MedialAxis.hpp b/xs/src/libslic3r/MedialAxis.hpp
index 560e2bf03..e4fd8e85d 100644
--- a/xs/src/libslic3r/MedialAxis.hpp
+++ b/xs/src/libslic3r/MedialAxis.hpp
@@ -5,6 +5,8 @@
 #include "ExPolygon.hpp"
 #include "Polyline.hpp"
 #include "Geometry.hpp"
+#include "ExtrusionEntityCollection.hpp"
+#include "Flow.hpp"
 #include <vector>
 
 #include "boost/polygon/voronoi.hpp"
@@ -58,6 +60,9 @@ namespace Slic3r {
         void remove_too_short_polylines(ThickPolylines& pp, const coord_t min_size);
         void ensure_not_overextrude(ThickPolylines& pp);
     };
+
+    ExtrusionEntityCollection thin_variable_width(const ThickPolylines &polylines, ExtrusionRole role, Flow flow);
+
 }
 
 
diff --git a/xs/src/libslic3r/PerimeterGenerator.cpp b/xs/src/libslic3r/PerimeterGenerator.cpp
index eeb60773c..7c60b7cff 100644
--- a/xs/src/libslic3r/PerimeterGenerator.cpp
+++ b/xs/src/libslic3r/PerimeterGenerator.cpp
@@ -282,6 +282,7 @@ void PerimeterGenerator::process()
                             no_thin_zone = diff_ex(last, offset_ex(half_thins, (float)(min_width / 2) - SCALED_EPSILON), true);
                         }
                         // compute a bit of overlap to anchor thin walls inside the print.
+                        ExPolygons thin_zones_extruded;
                         for (ExPolygon &half_thin : half_thins) {
                             //growing back the polygon
                             ExPolygons thin = offset_ex(half_thin, (float)(min_width / 2));
@@ -298,11 +299,13 @@ void PerimeterGenerator::process()
                                         // the maximum thickness of our thin wall area is equal to the minimum thickness of a single loop
                                         thin[0].medial_axis(bound, ext_perimeter_width + ext_perimeter_spacing2, min_width,
                                             &thin_walls, this->layer_height);
+                                        thin_zones_extruded.emplace_back(thin[0]);
                                     }
                                     break;
                                 }
                             }
                         }
+                        next_onion = diff_ex(offset_ex(last, -(float)(ext_perimeter_width / 2)), thin_zones_extruded, true);
                     }
                 } else {
                     //FIXME Is this offset correct if the line width of the inner perimeters differs
@@ -445,7 +448,7 @@ void PerimeterGenerator::process()
 
                 // append thin walls
                 if (!thin_walls.empty()) {
-                    ExtrusionEntityCollection tw = this->_variable_width
+                    ExtrusionEntityCollection tw = thin_variable_width
                         (thin_walls, erExternalPerimeter, this->ext_perimeter_flow);
 
                     entities.append(tw.entities);
@@ -485,7 +488,7 @@ void PerimeterGenerator::process()
                 }
             }
             if (!polylines.empty()) {
-                ExtrusionEntityCollection gap_fill = this->_variable_width(polylines, 
+                ExtrusionEntityCollection gap_fill = thin_variable_width(polylines, 
                     erGapFill, this->solid_infill_flow);
                 this->gap_fill->append(gap_fill.entities);
                 /*  Make sure we don't infill narrow parts that are already gap-filled
@@ -605,7 +608,7 @@ ExtrusionEntityCollection PerimeterGenerator::_traverse_loops(
     
     // append thin walls to the nearest-neighbor search (only for first iteration)
     if (!thin_walls.empty()) {
-        ExtrusionEntityCollection tw = this->_variable_width
+        ExtrusionEntityCollection tw = thin_variable_width
             (thin_walls, erExternalPerimeter, this->ext_perimeter_flow);
         
         coll.append(tw.entities);
@@ -1219,109 +1222,6 @@ PerimeterGenerator::_traverse_and_join_loops(const PerimeterGeneratorLoop &loop,
     return my_loop;
 }
 
-
-ExtrusionEntityCollection PerimeterGenerator::_variable_width(const ThickPolylines &polylines, ExtrusionRole role, Flow flow) const
-{
-    // this value determines granularity of adaptive width, as G-code does not allow
-    // variable extrusion within a single move; this value shall only affect the amount
-    // of segments, and any pruning shall be performed before we apply this tolerance
-    const double tolerance = scale_(0.05);
-    
-    int id_line = 0;
-    ExtrusionEntityCollection coll;
-    for (const ThickPolyline &p : polylines) {
-        id_line++;
-        ExtrusionPaths paths;
-        ExtrusionPath path(role);
-        ThickLines lines = p.thicklines();
-        
-        for (int i = 0; i < (int)lines.size(); ++i) {
-            const ThickLine& line = lines[i];
-            
-            const coordf_t line_len = line.length();
-            if (line_len < SCALED_EPSILON) continue;
-            
-            double thickness_delta = fabs(line.a_width - line.b_width);
-            if (thickness_delta > tolerance) {
-                const unsigned short segments = ceil(thickness_delta / tolerance);
-                const coordf_t seg_len = line_len / segments;
-                Points pp;
-                std::vector<coordf_t> width;
-                {
-                    pp.push_back(line.a);
-                    width.push_back(line.a_width);
-                    for (size_t j = 1; j < segments; ++j) {
-                        pp.push_back(line.point_at(j*seg_len));
-                        
-                        coordf_t w = line.a_width + (j*seg_len) * (line.b_width-line.a_width) / line_len;
-                        width.push_back(w);
-                        width.push_back(w);
-                    }
-                    pp.push_back(line.b);
-                    width.push_back(line.b_width);
-                    
-                    assert(pp.size() == segments + 1);
-                    assert(width.size() == segments*2);
-                }
-                
-                // delete this line and insert new ones
-                lines.erase(lines.begin() + i);
-                for (size_t j = 0; j < segments; ++j) {
-                    ThickLine new_line(pp[j], pp[j+1]);
-                    new_line.a_width = width[2*j];
-                    new_line.b_width = width[2*j+1];
-                    lines.insert(lines.begin() + i + j, new_line);
-                }
-                
-                --i;
-                continue;
-            }
-            
-            const double w = fmax(line.a_width, line.b_width);
-            if (path.polyline.points.empty()) {
-                path.polyline.append(line.a);
-                path.polyline.append(line.b);
-                // Convert from spacing to extrusion width based on the extrusion model
-                // of a square extrusion ended with semi circles.
-                flow.width = unscale(w) + flow.height * (1. - 0.25 * PI);
-                #ifdef SLIC3R_DEBUG
-                printf("  filling %f gap\n", flow.width);
-                #endif
-                path.mm3_per_mm  = flow.mm3_per_mm();
-                path.width       = flow.width;
-                path.height      = flow.height;
-            } else {
-                thickness_delta = fabs(scale_(flow.width) - w);
-                if (thickness_delta <= tolerance/2) {
-                    // the width difference between this line and the current flow width is 
-                    // within the accepted tolerance
-                    path.polyline.append(line.b);
-                } else {
-                    // we need to initialize a new line
-                    paths.emplace_back(std::move(path));
-                    path = ExtrusionPath(role);
-                    --i;
-                }
-            }
-        }
-        if (path.polyline.is_valid())
-            paths.emplace_back(std::move(path));        
-        // Append paths to collection.
-        if (!paths.empty()) {
-            if (paths.front().first_point().coincides_with(paths.back().last_point())) {
-                coll.append(ExtrusionLoop(paths));
-            } else {
-                //not a loop : avoid to "sort" it.
-                ExtrusionEntityCollection unsortable_coll(paths);
-                unsortable_coll.no_sort = true;
-                coll.append(unsortable_coll);
-            }
-        }
-    }
-
-    return coll;
-}
-
 bool PerimeterGeneratorLoop::is_internal_contour() const
 {
     // An internal contour is a contour containing no other contours
diff --git a/xs/src/libslic3r/PerimeterGenerator.hpp b/xs/src/libslic3r/PerimeterGenerator.hpp
index 0aae5bdb1..ecb6aa2ba 100644
--- a/xs/src/libslic3r/PerimeterGenerator.hpp
+++ b/xs/src/libslic3r/PerimeterGenerator.hpp
@@ -99,13 +99,10 @@ private:
     double _mm3_per_mm_overhang;
     Polygons _lower_slices_p;
 
-    ExtrusionEntityCollection _traverse_loops(const PerimeterGeneratorLoops &loops,
-        ThickPolylines &thin_walls) const;
+    ExtrusionEntityCollection _traverse_loops(const PerimeterGeneratorLoops &loops, ThickPolylines &thin_walls) const;
     ExtrusionLoop _traverse_and_join_loops(const PerimeterGeneratorLoop &loop, const PerimeterGeneratorLoops &childs, const Point entryPoint) const;
     ExtrusionLoop _extrude_and_cut_loop(const PerimeterGeneratorLoop &loop, const Point entryPoint, const Line &direction = Line(Point(0,0),Point(0,0))) const;
     PerimeterIntersectionPoint _get_nearest_point(const PerimeterGeneratorLoops &children, ExtrusionLoop &myPolylines, const coord_t dist_cut, const coord_t max_dist) const;
-    ExtrusionEntityCollection _variable_width
-        (const ThickPolylines &polylines, ExtrusionRole role, Flow flow) const;
 };
 
 }
diff --git a/xs/src/libslic3r/PrintConfig.cpp b/xs/src/libslic3r/PrintConfig.cpp
index 66bf3db2a..dfdb4e983 100644
--- a/xs/src/libslic3r/PrintConfig.cpp
+++ b/xs/src/libslic3r/PrintConfig.cpp
@@ -316,6 +316,7 @@ PrintConfigDef::PrintConfigDef()
     def->enum_keys_map = &ConfigOptionEnum<InfillPattern>::get_enum_values();
     def->enum_values.push_back("rectilinear");
     def->enum_values.push_back("concentric");
+    def->enum_values.push_back("concentricgapfill");
     def->enum_values.push_back("hilbertcurve");
     def->enum_values.push_back("archimedeanchords");
     def->enum_values.push_back("octagramspiral");
@@ -324,10 +325,11 @@ PrintConfigDef::PrintConfigDef()
     def->enum_values.push_back("smoothhilbert");
     def->enum_labels.push_back(L("Rectilinear"));
     def->enum_labels.push_back(L("Concentric"));
+    def->enum_labels.push_back(L("Concentric (filled)"));
     def->enum_labels.push_back(L("Hilbert Curve"));
     def->enum_labels.push_back(L("Archimedean Chords"));
     def->enum_labels.push_back(L("Octagram Spiral"));
-    def->enum_labels.push_back("Ironing");
+    def->enum_labels.push_back(L("Ironing"));
     // solid_fill_pattern is an obsolete equivalent to top_fill_pattern/bottom_fill_pattern.
     def->aliases = { "solid_fill_pattern" };
     def->default_value = new ConfigOptionEnum<InfillPattern>(ipRectilinear);
@@ -340,14 +342,16 @@ PrintConfigDef::PrintConfigDef()
     def->enum_keys_map = &ConfigOptionEnum<InfillPattern>::get_enum_values();
     def->enum_values.push_back("rectilinear");
     def->enum_values.push_back("concentric");
+    def->enum_values.push_back("concentricgapfill");
     def->enum_values.push_back("hilbertcurve");
     def->enum_values.push_back("archimedeanchords");
     def->enum_values.push_back("octagramspiral");
-    def->enum_labels.push_back("Rectilinear");
-    def->enum_labels.push_back("Concentric");
-    def->enum_labels.push_back("Hilbert Curve");
-    def->enum_labels.push_back("Archimedean Chords");
-    def->enum_labels.push_back("Octagram Spiral");
+    def->enum_labels.push_back(L("Rectilinear"));
+    def->enum_labels.push_back(L("Concentric"));
+    def->enum_labels.push_back(L("Concentric (filled)"));
+    def->enum_labels.push_back(L("Hilbert Curve"));
+    def->enum_labels.push_back(L("Archimedean Chords"));
+    def->enum_labels.push_back(L("Octagram Spiral"));
     def->default_value = new ConfigOptionEnum<InfillPattern>(ipRectilinear);
 
     def = this->add("enforce_full_fill_volume", coBool);
@@ -819,6 +823,7 @@ PrintConfigDef::PrintConfigDef()
     def->enum_values.push_back("cubic");
     def->enum_values.push_back("line");
     def->enum_values.push_back("concentric");
+    def->enum_values.push_back("concentricgapfill");
     def->enum_values.push_back("honeycomb");
     def->enum_values.push_back("3dhoneycomb");
     def->enum_values.push_back("gyroid");
@@ -832,6 +837,7 @@ PrintConfigDef::PrintConfigDef()
     def->enum_labels.push_back(L("Cubic"));
     def->enum_labels.push_back(L("Line"));
     def->enum_labels.push_back(L("Concentric"));
+    def->enum_labels.push_back(L("Concentric (filled)"));
     def->enum_labels.push_back(L("Honeycomb"));
     def->enum_labels.push_back(L("3D Honeycomb"));
     def->enum_labels.push_back(L("Gyroid"));
diff --git a/xs/src/libslic3r/PrintConfig.hpp b/xs/src/libslic3r/PrintConfig.hpp
index 4dc2d95c8..9884b1c50 100644
--- a/xs/src/libslic3r/PrintConfig.hpp
+++ b/xs/src/libslic3r/PrintConfig.hpp
@@ -34,7 +34,7 @@ enum PrintHostType {
 enum InfillPattern {
     ipRectilinear, ipGrid, ipTriangles, ipStars, ipCubic, ipLine, ipConcentric, ipHoneycomb, ip3DHoneycomb,
     ipGyroid, ipHilbertCurve, ipArchimedeanChords, ipOctagramSpiral, ipSmooth, ipSmoothHilbert, ipSmoothTriple,
-    ipRectiWithPerimeter,
+    ipRectiWithPerimeter, ipConcentricGapFill
 };
 
 enum SupportMaterialPattern {
@@ -89,6 +89,7 @@ template<> inline t_config_enum_values& ConfigOptionEnum<InfillPattern>::get_enu
         keys_map["cubic"]               = ipCubic;
         keys_map["line"]                = ipLine;
         keys_map["concentric"]          = ipConcentric;
+        keys_map["concentricgapfill"]   = ipConcentricGapFill;
         keys_map["honeycomb"]           = ipHoneycomb;
         keys_map["3dhoneycomb"]         = ip3DHoneycomb;
         keys_map["gyroid"]              = ipGyroid;
diff --git a/xs/src/libslic3r/SupportMaterial.cpp b/xs/src/libslic3r/SupportMaterial.cpp
index 404f3e2c9..bbca3eb27 100644
--- a/xs/src/libslic3r/SupportMaterial.cpp
+++ b/xs/src/libslic3r/SupportMaterial.cpp
@@ -3098,7 +3098,7 @@ void PrintObjectSupportMaterial::generate_toolpaths(
         size_t idx_layer_top_contact      = size_t(-1);
         size_t idx_layer_intermediate     = size_t(-1);
         size_t idx_layer_inteface         = size_t(-1);
-        std::unique_ptr<Fill> filler_interface = std::unique_ptr<Fill>(Fill::new_from_type(m_slicing_params.soluble_interface ? ipConcentric : ipRectilinear));
+        std::unique_ptr<Fill> filler_interface = std::unique_ptr<Fill>(Fill::new_from_type(m_slicing_params.soluble_interface ? ipConcentricGapFill : ipRectilinear));
         std::unique_ptr<Fill> filler_support = std::unique_ptr<Fill>(Fill::new_from_type(infill_pattern));
         std::unique_ptr<Fill> filler_solid = std::unique_ptr<Fill>(Fill::new_from_type(ipRectiWithPerimeter));
         filler_interface->set_bounding_box(bbox_object);