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Infill Patterns

The infill module generates interior fill patterns for 3D printed parts. Infill provides structural strength while using less material than solid fills.

Overview

Polyslice supports seven infill patterns:

  • Grid: Crosshatch pattern at ±45° angles
  • Triangles: Tessellation of equilateral triangles
  • Hexagons: Honeycomb pattern for optimal strength-to-weight ratio
  • Concentric: Inward-spiraling contours following the part shape
  • Gyroid: Wavy TPMS structure for excellent strength and isotropy
  • Spiral: Outward-spiraling Archimedean spiral from center
  • Lightning: Tree-like branching structure for fast, minimal material infill

Usage

const Polyslice = require("@jgphilpott/polyslice");

const slicer = new Polyslice({
    infillDensity: 20,       // 20% infill
    infillPattern: "grid",   // Pattern type
    nozzleTemperature: 200,
    bedTemperature: 60
});

// Slice a mesh - infill is generated automatically
const gcode = slicer.slice(mesh);

Configuration Options

const slicer = new Polyslice({
    // Infill density (0-100%)
    // 0 = hollow, 100 = solid
    infillDensity: 20,

    // Infill pattern type
    // Options: "grid", "triangles", "hexagons", "concentric", "gyroid", "spiral", "lightning"
    infillPattern: "grid",

    // Pattern centering mode
    // Options: "object" (center on object boundary) or "global" (center on build plate)
    infillPatternCentering: "object",

    // Infill speed in mm/s
    infillSpeed: 60,

    // Nozzle diameter affects line spacing
    nozzleDiameter: 0.4
});

Pattern Centering Modes

Polyslice provides two modes for centering infill patterns:

Object Centering (default, "object"):

  • Each object has its own pattern center
  • Patterns are centered on each object's boundary
  • Good for ensuring consistent infill within each part
  • Best for most prints

Global Centering ("global"):

  • All objects share the same pattern grid
  • Pattern is centered on the build plate center
  • Good for multi-object prints where pattern alignment across parts matters
  • May result in incomplete pattern coverage at object edges depending on position
// Object centering (default)
slicer.setInfillPatternCentering("object");

// Global centering
slicer.setInfillPatternCentering("global");

When to use object centering:

  • Single object prints
  • Multi-object prints where each part should have complete pattern coverage
  • When you want consistent infill regardless of object position

When to use global centering:

  • Multi-object prints where pattern alignment across parts is important
  • When printing parts that will be assembled and you want matching infill phases
  • When you want a consistent grid across the entire build plate

Available Patterns

Grid Pattern

The grid pattern creates a crosshatch fill using two sets of lines at +45° and -45° angles.

    ╲ ╱ ╲ ╱ ╲ ╱
     ╳   ╳   ╳
    ╱ ╲ ╱ ╲ ╱ ╲
   ╳   ╳   ╳   ╳
    ╲ ╱ ╲ ╱ ╲ ╱

Characteristics:

  • Simple and fast to print
  • Good for general-purpose parts
  • Equal strength in X and Y directions
  • Lines intersect at 90° angles

Best for:

  • Prototypes
  • Non-structural parts
  • Quick prints where strength is not critical

Line Spacing Formula:

spacing = (nozzleDiameter / (density / 100)) * 2

For example, at 20% density with 0.4mm nozzle:

  • spacing = (0.4 / 0.2) * 2 = 4.0mm per direction
  • Each direction provides 10% density, totaling 20%

Triangles Pattern

The triangles pattern creates a tessellation of equilateral triangles using three line sets spaced 60° apart. The baseline runs at 45°, with additional lines at +60° (105°) and -60° (-15°) from the baseline.

      /\    /\
     /  \  /  \
    /    \/    \
    \    /\    /
     \  /  \  /
      \/    \/

Characteristics:

  • Strong in all directions (isotropic)
  • Better load distribution than grid
  • Slightly slower print time
  • Three line sets create equilateral triangles

Best for:

  • Parts requiring uniform strength
  • Load-bearing components
  • Structural prototypes

Line Spacing Formula:

spacing = (nozzleDiameter / (density / 100)) * 3

For example, at 20% density with 0.4mm nozzle:

  • spacing = (0.4 / 0.2) * 3 = 6.0mm per direction
  • Each of three directions provides ~6.67% density, totaling 20%

Hexagons Pattern

The hexagons pattern creates a honeycomb-like structure with actual hexagonal cells.

    ___     ___
   /   \___/   \
   \___/   \___/
   /   \___/   \
   \___/   \___/

Characteristics:

  • Excellent strength-to-weight ratio
  • Natural structural efficiency (like bee honeycombs)
  • Optimal for compression loads
  • More complex path planning

Best for:

  • Lightweight structural parts
  • Aerospace and automotive applications
  • Parts requiring high strength with minimum material
  • Load-bearing surfaces

Cell Sizing: The hexagon size is derived from line spacing:

hexagonSide = lineSpacing / sqrt(3)
horizontalSpacing = hexagonSide * sqrt(3)
verticalSpacing = hexagonSide * 1.5

Concentric Pattern

The concentric pattern creates inward-spiraling contours that follow the natural shape of the part.

    __________
   /          \
  /  ________  \
 / /          \ \
| |  ______  | |
| | |      | | |
| | |______| | |
 \ \________/ /
  \__________/

Characteristics:

  • Follows the natural contour of the part
  • Each layer independently adapts to the shape
  • Continuous extrusion paths (minimal retractions)
  • Excellent for cylindrical or curved parts

Best for:

  • Parts with circular or curved cross-sections
  • Cylinders, tubes, and rounded shapes
  • When you want the infill to follow the part geometry
  • Decorative patterns where concentric lines are desired

Line Spacing Formula:

spacing = nozzleDiameter / (density / 100)

For example, at 20% density with 0.4mm nozzle:

  • spacing = 0.4 / 0.2 = 2.0mm between loops
  • Creates concentric loops at 2mm intervals

Pattern Generation: The concentric pattern works by repeatedly insetting (offsetting inward) the boundary:

  1. Start at the infill boundary
  2. Generate a contour loop
  3. Inset by line spacing
  4. Repeat until the center is reached

Note: The infillPatternCentering setting does not affect the concentric pattern. Concentric infill always follows the part's boundary contours rather than a fixed grid, so it will conform to the model shape regardless of the configured centering mode.

Gyroid Pattern

The gyroid pattern creates a wavy structure that approximates a triply periodic minimal surface (TPMS). This results in excellent strength-to-weight ratio with isotropic properties.

    ~~~  ~~~  ~~~
   ~  ~~  ~~  ~~
  ~  ~  ~~  ~~  ~
 ~~  ~~  ~~  ~~
~~~  ~~~  ~~~

Characteristics:

  • Wavy lines create smooth 3D structure
  • Excellent strength in all directions (isotropic)
  • Better load distribution than grid
  • Comparable to hexagons for structural efficiency
  • Natural appearance with organic flowing lines
  • More G-code commands than straight-line patterns (due to wavy paths)
  • Gradual direction transition over 8-layer cycles for improved interlayer adhesion

Best for:

  • High-performance functional parts
  • Parts requiring uniform strength in all directions
  • Aerospace and engineering applications
  • Structural components with compression and tension loads
  • Parts where strength-to-weight ratio is critical

Line Spacing Formula:

spacing = (nozzleDiameter / (density / 100)) * 1.5

For example, at 20% density with 0.4mm nozzle:

  • spacing = (0.4 / 0.2) * 1.5 = 3.0mm
  • Wave amplitude is 40% of line spacing
  • Direction gradually transitions over 8 layers

Pattern Generation: The gyroid pattern uses mathematical wave functions based on the gyroid minimal surface equation:

  1. Calculate phase offset based on Z height
  2. Calculate rotation angle for current layer (0° to 90° over 8-layer cycle)
  3. Generate ONE set of wavy lines at the calculated rotation angle
  4. Apply sine/cosine functions for wave displacement
  5. Create 3D interlocking structure across layers

Rotation Behavior: Each layer has exactly ONE set of wavy lines that gradually rotates:

  • Layer 0 (0.0°): Horizontal wavy lines (~92 lines)
  • Layer 1 (11.25°): Slightly rotated (~84 lines)
  • Layer 2 (22.5°): More rotated (~95 lines)
  • Layer 3 (33.75°): Diagonal (~92 lines)
  • Layer 4 (45.0°): 45° diagonal (~98 lines)
  • Layer 5 (56.25°): More vertical (~100 lines)
  • Layer 6 (67.5°): Near vertical (~91 lines)
  • Layer 7 (78.75°): Almost vertical (~88 lines)
  • Layer 8: Cycle repeats (0° again)

This creates smooth layer-to-layer transitions with consistent material usage.

Spiral Pattern

The spiral pattern creates a continuous Archimedean spiral from the center outward.

      ___---~~~
    /          \
   |    ____    |
   |  /    \    |
   | |  •   |   |
   |  \____/    |
    \          /
     ~~~---___

Characteristics:

  • Continuous single path from center to edge
  • Smooth circular motion following spiral curve
  • Consistent spacing between turns
  • Natural fit for cylindrical or circular parts
  • Minimal travel moves (continuous extrusion)
  • Simple and predictable pattern

Best for:

  • Cylindrical parts (tubes, bottles, cups)
  • Circular cross-sections
  • Parts where continuous extrusion is desired
  • Decorative pieces with spiral aesthetic
  • Fast printing with minimal retractions

Line Spacing Formula:

spacing = nozzleDiameter / (density / 100)

For example, at 20% density with 0.4mm nozzle:

  • spacing = 0.4 / 0.2 = 2.0mm between spiral turns
  • Creates smooth Archimedean spiral with consistent spacing

Pattern Generation: The spiral pattern uses parametric equations of an Archimedean spiral:

  1. Calculate maximum radius needed to cover boundary
  2. Generate spiral path: r = (spacing / 2π) × θ
  3. Convert to Cartesian coordinates: x = r × cos(θ), y = r × sin(θ)
  4. Clip spiral segments to infill boundary

Lightning Pattern

The lightning pattern creates a tree-like branching structure for fast printing with minimal material usage.

    \  |  /     \  |  /
     \ | /       \ | /
      \|/         \|/
       |           |
       |           |
━━━━━━━━━━━━━━━━━━━━━

Characteristics:

  • Tree-like branches extending from boundary inward
  • Each branch forks into sub-branches for support
  • Very fast printing (minimal material)
  • Adequate support for top layers
  • Natural, organic appearance
  • Branches directed toward center with angle variation

Best for:

  • Prototypes where speed is critical
  • Non-structural decorative parts
  • Quick test prints
  • Models where minimal infill is acceptable
  • Parts where top surface quality is more important than strength

Line Spacing Formula:

spacing = (nozzleDiameter / (density / 100)) * 2.0

For example, at 20% density with 0.4mm nozzle:

  • lineSpacing = (0.4 / 0.2) * 2.0 = 4.0mm
  • branchSpacing = lineSpacing * 2.5 = 10.0mm between branch starting points
  • Branches extend approximately 80% of the smaller dimension
  • Sub-branches fork at 40% of main branch length at 45° angles

Pattern Generation: The lightning pattern algorithm:

  1. Calculate branch starting points along the boundary perimeter (spaced by lineSpacing * 2.5)
  2. Direct main branches toward the center with angle variation
  3. Create forking sub-branches at midpoints (45° from main direction)
  4. Clip all branches to stay within the infill boundary
  5. Avoid hole regions using clipping algorithm

Density Guide

Density Use Case
0% Hollow - vases, decorative items
5-10% Light structural support
15-20% Standard - most prints (recommended)
25-35% Functional parts with moderate stress
40-60% High-strength mechanical parts
70-90% Near-solid for maximum strength
100% Solid - heavy-duty applications

Pattern Comparison

Feature Grid Triangles Hexagons Concentric Gyroid Spiral Lightning
Print Speed ★★★★★ ★★★★ ★★★ ★★★★ ★★★ ★★★★★ ★★★★★
X/Y Strength ★★★ ★★★★ ★★★★ ★★★ ★★★★★ ★★ ★★
Compression ★★★ ★★★★ ★★★★★ ★★★ ★★★★★ ★★ ★
Material Use ★★★ ★★★ ★★★★ ★★★★ ★★★★ ★★★★ ★★★★★
Complexity ★ ★★ ★★★ ★ ★★ ★ ★★
Curved Parts ★★ ★★ ★★ ★★★★★ ★★★ ★★★★★ ★★★
Isotropy ★★ ★★★★ ★★★★ ★★ ★★★★★ ★ ★

Technical Details

Infill Generation Process

  1. Boundary Calculation: Create an inset from the innermost wall (half nozzle gap)
  2. Hole Exclusion: Subtract hole regions from infill area
  3. Skin Exclusion: On mixed layers, exclude skin areas from infill
  4. Pattern Generation: Generate line segments based on selected pattern
  5. Clipping: Clip lines against boundary polygon
  6. Travel Optimization: Use combing to avoid crossing holes

Combing Integration

All infill patterns use travel path optimization (combing) to avoid crossing holes:

  • Lines are sorted by position to minimize travel distance
  • Travel moves route around holes using waypoints
  • This prevents stringing artifacts in printed holes

See COMBING.md for details on travel path optimization.

Skin Interaction

On layers with adaptive skin (exposed surfaces):

  1. Skin areas are subtracted from the infill boundary
  2. Infill is generated in non-skin regions
  3. Skin is printed after infill (so skin covers infill pattern)

See EXPOSURE_DETECTION.md for adaptive skin details.

File Structure

src/slicer/infill/
├── infill.coffee            # Main infill coordination
├── infill.test.coffee       # Infill tests
└── patterns/
    ├── grid.coffee          # Grid pattern implementation
    ├── grid.test.coffee
    ├── triangles.coffee     # Triangles pattern implementation
    ├── triangles.test.coffee
    ├── hexagons.coffee      # Hexagons pattern implementation
    ├── hexagons.test.coffee
    ├── concentric.coffee    # Concentric pattern implementation
    ├── concentric.test.coffee
    ├── gyroid.coffee        # Gyroid pattern implementation
    ├── gyroid.test.coffee
    ├── spiral.coffee        # Spiral pattern implementation
    ├── spiral.test.coffee
    ├── lightning.coffee     # Lightning pattern implementation
    └── lightning.test.coffee

API Reference

Slicer Configuration

// Get/set infill density (0-100)
slicer.setInfillDensity(20);
const density = slicer.getInfillDensity();

// Get/set infill pattern
slicer.setInfillPattern("hexagons");
const pattern = slicer.getInfillPattern();

// Get/set pattern centering mode
slicer.setInfillPatternCentering("object"); // or "global"
const centering = slicer.getInfillPatternCentering();

// Get/set infill speed (mm/s)
slicer.setInfillSpeed(60);
const speed = slicer.getInfillSpeed();

Pattern Values

// Valid pattern values
"grid"       // Crosshatch at ±45°
"triangles"  // Equilateral triangle tessellation
"hexagons"   // Honeycomb pattern
"concentric" // Inward-spiraling contours
"gyroid"     // Wavy TPMS structure
"spiral"     // Outward-spiraling from center
"lightning"  // Tree-like branching structure

Centering Values

// Valid centering values
"object"     // Center pattern on each object's boundary (default)
"global"     // Center pattern on build plate center

Future Patterns

The following patterns may be added in future versions:

  • Lines: Single direction linear fill
  • Cubic: 3D interlocking cubes

Tips

  1. Start with 20% grid for most prints - it's fast and adequate for non-structural parts

  2. Use hexagons for parts that need to be strong but lightweight

  3. Use lightning for rapid prototyping and test prints where speed is critical

  4. Increase density for functional parts that will bear loads

  5. Consider print time: Grid and lightning are fastest, hexagons is slowest

  6. Test your material: Some materials (like TPU) may require higher infill for flexibility

  7. Top/bottom layers: Solid skin layers cover the infill pattern on visible surfaces