diff --git a/src/settings/default.yml b/src/settings/default.yml
index 694cf51..d337f04 100644
--- a/src/settings/default.yml
+++ b/src/settings/default.yml
@@ -37,7 +37,7 @@ outerShell:
   speed: 40.0
 innerInfill:
   flowRate: 1.0
-  speed: 50.0
+  speed: 80.0
   gridSize: 5.0
 outerInfill:
   flowRate: 1.0
diff --git a/src/sliceActions/generateInfills.js b/src/sliceActions/generateInfills.js
index 14c5f66..1b87787 100644
--- a/src/sliceActions/generateInfills.js
+++ b/src/sliceActions/generateInfills.js
@@ -34,39 +34,35 @@ export default function generateInfills(slices, settings) {
     for (let i = 0; i < slice.parts.length; i ++) {
       const part = slice.parts[i];
 
-      if (!part.shape.closed) {
-        continue;
+      if (!part.shape.closed) continue;
+
+      const innerShell = part.shell[part.shell.length - 1];
+
+      if (innerShell.paths.length === 0) continue;
+
+      const fillArea = innerShell.offset(-nozzleRadius);
+      let innerFillArea;
+      let outerFillArea;
+      if (surroundingLayer) {
+        outerFillArea = fillArea.difference(surroundingLayer).intersect(fillArea);
+        innerFillArea = fillArea.difference(outerFillArea);
+      } else {
+        outerFillArea = fillArea;
       }
 
-      const outerLine = part.outerLine;
+      if (innerFillArea && innerFillArea.paths.length > 0) {
+        const bounds = innerFillArea.shapeBounds();
+        const innerFillTemplate = getFillTemplate(bounds, infillGridSize, true, true);
 
-      if (outerLine.paths.length > 0) {
-        const inset = (part.innerLines.length > 0) ? part.innerLines[part.innerLines.length - 1] : outerLine;
+        part.innerFill.join(innerFillTemplate.intersect(innerFillArea));
+      }
 
-        const fillArea = inset.offset(-nozzleRadius);
-        let innerFillArea;
-        let outerFillArea;
-        if (surroundingLayer) {
-          outerFillArea = fillArea.difference(surroundingLayer).intersect(fillArea);
-          innerFillArea = fillArea.difference(outerFillArea);
-        } else {
-          outerFillArea = fillArea;
-        }
+      if (outerFillArea.paths.length > 0) {
+        const bounds = outerFillArea.shapeBounds();
+        const even = (layer % 2 === 0);
+        const outerFillTemplate = getFillTemplate(bounds, outerFillTemplateSize, even, !even);
 
-        if (innerFillArea && innerFillArea.paths.length > 0) {
-          const bounds = innerFillArea.shapeBounds();
-          const innerFillTemplate = getFillTemplate(bounds, infillGridSize, true, true);
-
-          part.innerFill.join(innerFillTemplate.intersect(innerFillArea));
-        }
-
-        if (outerFillArea.paths.length > 0) {
-          const bounds = outerFillArea.shapeBounds();
-          const even = (layer % 2 === 0);
-          const outerFillTemplate = getFillTemplate(bounds, outerFillTemplateSize, even, !even);
-
-          part.outerFill.join(outerFillTemplate.intersect(outerFillArea));
-        }
+        part.outerFill.join(outerFillTemplate.intersect(outerFillArea));
       }
     }
   }
diff --git a/src/sliceActions/generateInnerLines.js b/src/sliceActions/generateInnerLines.js
index 2da441a..c2767c7 100644
--- a/src/sliceActions/generateInnerLines.js
+++ b/src/sliceActions/generateInnerLines.js
@@ -19,7 +19,7 @@ export default function generateInnerLines(slices, settings) {
   shellThickness /= PRECISION;
 
   const nozzleRadius = nozzleDiameter / 2;
-  const shells = Math.round(shellThickness / nozzleDiameter);
+  const numShells = Math.round(shellThickness / nozzleDiameter);
 
   for (let layer = 0; layer < slices.length; layer ++) {
     const slice = slices[layer];
@@ -32,16 +32,16 @@ export default function generateInnerLines(slices, settings) {
       const outerLine = part.shape.offset(-nozzleRadius, offsetOptions);
 
       if (outerLine.paths.length > 0) {
-        part.outerLine.join(outerLine);
+        part.shell.push(outerLine);
 
         // start with 1 because outerLine is the 1st (0) shell
-        for (let shell = 1; shell < shells; shell += 1) {
-          const offset = shell * nozzleDiameter;
+        for (let inset = 1; inset < numShells; inset += 1) {
+          const offset = inset * nozzleDiameter;
 
-          const innerLine = outerLine.offset(-offset, offsetOptions);
+          const shell = outerLine.offset(-offset, offsetOptions);
 
-          if (innerLine.paths.length > 0) {
-            part.innerLines.push(innerLine);
+          if (shell.paths.length > 0) {
+            part.shell.push(shell);
           } else {
             break;
           }
diff --git a/src/sliceActions/generateOutlines.js b/src/sliceActions/generateOutlines.js
index 9fca57b..b3609db 100644
--- a/src/sliceActions/generateOutlines.js
+++ b/src/sliceActions/generateOutlines.js
@@ -5,7 +5,10 @@ export default function calculateOutlines(slices, settings) {
     const slice = slices[layer];
 
     slice.outline = slice.parts.reduce((shape, part) => {
-      if (part.outerLine) shape.join(part.outerLine);
+      if (part.shape.closed) {
+        const [outerLine] = part.shell;
+        shape.join(outerLine);
+      }
       return shape;
     }, new Shape([], true));
   }
diff --git a/src/sliceActions/helpers/Slice.js b/src/sliceActions/helpers/Slice.js
index ee966ff..b02c6ab 100644
--- a/src/sliceActions/helpers/Slice.js
+++ b/src/sliceActions/helpers/Slice.js
@@ -8,8 +8,7 @@ export default class {
     const part = { shape };
 
     if (shape.closed) {
-      part.innerLines = [];
-      part.outerLine = new Shape([], true);
+      part.shell = [];
       part.innerFill = new Shape([], false);
       part.outerFill = new Shape([], false);
     }
diff --git a/src/sliceActions/optimizePaths.js b/src/sliceActions/optimizePaths.js
index 8f67786..dd249a2 100644
--- a/src/sliceActions/optimizePaths.js
+++ b/src/sliceActions/optimizePaths.js
@@ -17,7 +17,7 @@ export default function optimizePaths(slices, settings) {
     for (let i = 0; i < slice.parts.length; i ++) {
       const part = slice.parts[i];
 
-      const shape = part.shape.closed ? part.outerLine : part.shape;
+      const shape = part.shape.closed ? part.shell[0] : part.shape;
       const bounds = shape.shapeBounds();
 
       boundingBoxes.set(part, bounds);
@@ -48,9 +48,13 @@ export default function optimizePaths(slices, settings) {
       parts.push(part);
 
       if (part.shape.closed) {
-        if (part.innerFill.paths.length > 0) {
-          part.innerFill = optimizeShape(part.innerFill, start);
-          start.copy(part.innerFill.lastPoint(true));
+        for (let i = 0; i < part.shell.length; i ++) {
+          const shell = part.shell[i];
+
+          if (shell.paths.length === 0) continue;
+
+          part.shell[i] = optimizeShape(shell, start);
+          start.copy(part.shell[i].lastPoint(true));
         }
 
         if (part.outerFill.paths.length > 0) {
@@ -58,18 +62,9 @@ export default function optimizePaths(slices, settings) {
           start.copy(part.outerFill.lastPoint(true));
         }
 
-        for (let i = 0; i < part.innerLines.length; i ++) {
-          const innerLine = part.innerLines[i];
-
-          if (innerLine.paths.length > 0) {
-            part.innerLines[i] = optimizeShape(innerLine, start);
-            start.copy(part.innerLines[i].lastPoint(true));
-          }
-        }
-
-        if (part.outerLine.paths.length > 0) {
-          part.outerLine = optimizeShape(part.outerLine, start);
-          start.copy(part.outerLine.lastPoint(true));
+        if (part.innerFill.paths.length > 0) {
+          part.innerFill = optimizeShape(part.innerFill, start);
+          start.copy(part.innerFill.lastPoint(true));
         }
       } else {
         part.shape = optimizeShape(part.shape, start);
diff --git a/src/sliceActions/removePrecision.js b/src/sliceActions/removePrecision.js
index f84ce05..ccc8466 100644
--- a/src/sliceActions/removePrecision.js
+++ b/src/sliceActions/removePrecision.js
@@ -10,9 +10,8 @@ export default function removePrecision(slices) {
       const part = slice.parts[i];
 
       if (part.shape.closed) {
-        part.outerLine.scaleDown(inversePrecision);
-        for (let i = 0; i < part.innerLines.length; i ++) {
-          const innerLine = part.innerLines[i];
+        for (let i = 0; i < part.shell.length; i ++) {
+          const innerLine = part.shell[i];
           innerLine.scaleDown(inversePrecision);
         }
         part.innerFill.scaleDown(inversePrecision);
diff --git a/src/sliceActions/slicesToGCode.js b/src/sliceActions/slicesToGCode.js
index 9ae9194..b14e9d4 100644
--- a/src/sliceActions/slicesToGCode.js
+++ b/src/sliceActions/slicesToGCode.js
@@ -49,15 +49,17 @@ export default function slicesToGCode(slices, settings) {
       const part = slice.parts[i];
 
       if (part.shape.closed) {
-        pathToGCode(gcode, part.innerFill, false, true, z, profiles.innerInfill);
-        pathToGCode(gcode, part.outerFill, false, false, z, profiles.outerInfill);
+        for (let i = 0; i < part.shell.length; i ++) {
+          const shell = part.shell[i];
+          const isOuterShell = i === 0;
 
-        for (let i = 0; i < part.innerLines.length; i ++) {
-          const innerLine = part.innerLines[i];
-          pathToGCode(gcode, innerLine, false, false, z, profiles.innerShell);
+          const unRetract = isOuterShell;
+          const profile = isOuterShell ? profiles.outerShell : profiles.innerShell;
+          pathToGCode(gcode, shell, false, unRetract, z, profile);
         }
 
-        pathToGCode(gcode, part.outerLine, true, false, z, profiles.outerShell);
+        pathToGCode(gcode, part.outerFill, false, false, z, profiles.outerInfill);
+        pathToGCode(gcode, part.innerFill, true, false, z, profiles.innerInfill);
       } else {
         const retract = !(slice.parts.length === 1 && typeof slice.support === 'undefined');
         pathToGCode(gcode, part.shape, retract, retract, z, profiles.outerShell);