diff --git a/src/settings/default.yml b/src/settings/default.yml
index 77db94c..0fd05a0 100644
--- a/src/settings/default.yml
+++ b/src/settings/default.yml
@@ -35,7 +35,6 @@ innerLine:
 fill:
   flowRate: 1.0
   speed: 50.0
-  overlap: 0.0
   gridSize: 5.0
 brim:
   flowRate: 1.0
diff --git a/src/sliceActions/generateInfills.js b/src/sliceActions/generateInfills.js
index 40ed2a6..31c4ec7 100644
--- a/src/sliceActions/generateInfills.js
+++ b/src/sliceActions/generateInfills.js
@@ -8,8 +8,7 @@ export default function generateInfills(slices, settings) {
     fill: { gridSize: fillGridSize },
     bottom: { thickness: bottomThickness },
     top: { thickness: topThickness },
-    nozzleDiameter,
-    fill: { overlap: infillOverlap }
+    nozzleDiameter
   } = settings;
 
   fillGridSize /= PRECISION;
@@ -47,13 +46,7 @@ export default function generateInfills(slices, settings) {
         let lowFillArea;
         let highFillArea;
         if (surroundingLayer) {
-          highFillArea = fillArea.difference(surroundingLayer);
-
-          if (infillOverlap > 0) {
-            highFillArea = highFillArea.offset(infillOverlap);
-          }
-
-          highFillArea = highFillArea.intersect(fillArea);
+          highFillArea = fillArea.difference(surroundingLayer).intersect(fillArea);
           lowFillArea = fillArea.difference(highFillArea);
         } else {
           highFillArea = fillArea;
diff --git a/src/sliceActions/generateInnerLines.js b/src/sliceActions/generateInnerLines.js
index 046369c..cfab81e 100644
--- a/src/sliceActions/generateInnerLines.js
+++ b/src/sliceActions/generateInnerLines.js
@@ -32,7 +32,8 @@ export default function generateInnerLines(slices, settings) {
       if (outerLine.paths.length > 0) {
         part.outerLine.join(outerLine);
 
-        for (let shell = 1; shell <= shells; shell += 1) {
+        // start with 1 because outerLine is the 1st (0) shell
+        for (let shell = 1; shell < shells; shell += 1) {
           const offset = shell * nozzleDiameter;
 
           const innerLine = outerLine.offset(-offset, offsetOptions);
diff --git a/src/sliceActions/helpers/GCode.js b/src/sliceActions/helpers/GCode.js
index 18f0261..48bc6dc 100644
--- a/src/sliceActions/helpers/GCode.js
+++ b/src/sliceActions/helpers/GCode.js
@@ -107,7 +107,7 @@ export default class {
     const lineLength = this._nozzlePosition.distanceTo(newNozzlePosition);
 
     const filamentSurfaceArea = Math.pow((filamentThickness / 2), 2) * Math.PI;
-    this._extruder += lineLength * nozzleDiameter * layerHeight / filamentSurfaceArea * flowRate;
+    this._extruder += lineLength * ((nozzleDiameter * layerHeight) / filamentSurfaceArea) * flowRate;
 
     this._addGCode({
       [MOVE]: 1,
@@ -164,7 +164,7 @@ export default class {
 
       const speed = retractionSpeed * 60;
 
-      if (this._extruder > retractionMinDistance && retractionEnabled) {
+      if (this._extruder > retractionMinDistance) {
         this._addGCode({
           [MOVE]: 0,
           [EXTRUDER]: (this._extruder - retractionAmount).toFixed(3),
diff --git a/src/sliceActions/optimizePaths.js b/src/sliceActions/optimizePaths.js
index 6cc861c..5c6e718 100644
--- a/src/sliceActions/optimizePaths.js
+++ b/src/sliceActions/optimizePaths.js
@@ -13,6 +13,15 @@ export default function optimizePaths(slices, settings) {
     }
 
     const parts = [];
+    const boundingBoxes = new WeakMap();
+    for (let i = 0; i < slice.parts.length; i ++) {
+      const part = slice.parts[i];
+
+      const shape = part.shape.closed ? part.outerLine : part.shape;
+      const bounds = shape.shapeBounds();
+
+      boundingBoxes.set(part, bounds);
+    }
 
     while (slice.parts.length > 0) {
       let closestDistance = Infinity;
@@ -20,16 +29,14 @@ export default function optimizePaths(slices, settings) {
 
       for (let i = 0; i < slice.parts.length; i ++) {
         const part = slice.parts[i];
+        const bounds = boundingBoxes.get(part);
 
-        const shape = part.shape.closed ? part.outerLine : part.shape;
-        const bounds = shape.shapeBounds();
+        const topDistance = bounds.top - start.y;
+        const bottomDistance = start.y - bounds.bottom;
+        const leftDistance = bounds.left - start.x;
+        const rightDistance = start.x - bounds.right;
 
-        const top = bounds.top - start.y;
-        const bottom = start.y - bounds.bottom;
-        const left = bounds.left - start.x;
-        const right = start.x - bounds.right;
-
-        const distance = Math.max(top, bottom, left, right);
+        const distance = Math.max(topDistance, bottomDistance, leftDistance, rightDistance);
 
         if (distance < closestDistance) {
           closestDistance = distance;