Printing Guide

Infill Patterns

Infill is the internal structure of your print. The right pattern and percentage can mean the difference between a part that lasts years and one that snaps on first use.

What Infill Actually Does

Infill fills the interior of printed parts - not to make them solid, but to support top surfaces and add internal structure. The percentage refers to what fraction of the interior volume is filled. 20% infill means 80% of the interior is air.

Contrary to intuition, increasing infill past ~40% has diminishing strength returns. [1] Adding more walls (perimeters) is almost always more effective for strength than increasing infill.

Infill %

What percentage of interior is filled. 10-15% for visual, 20-30% for functional, 40%+ for load-bearing.

Wall Interaction

Walls carry most structural load. Infill mainly supports top surfaces and adds compression resistance.

Print Time

Infill is often the largest time factor. Cutting from 30% to 15% can save 10-20% print time.

Strength Rule

Adding one more wall perimeter is usually stronger per minute of print time than raising infill by 10%. [1]

Relative Strength vs Infill Percentage

Relative part strength increases rapidly up to ~40% infill, then additional material yields minimal strength gains. Adding more wall perimeters is usually more effective past this point.

Tips

The "4 walls + 15% gyroid" rule: for most functional parts, 4 wall perimeters with 15-20% gyroid infill outperforms 2 walls with 40% grid in both strength and print time. [1]

Infill percentage does not affect surface appearance - top surface quality is controlled by top layer count and infill contact points, not infill density alone.

Pattern Reference

Thirteen patterns worth knowing - what each looks like, what it's strong at, and when to use it.

Grid

Medium Speed XY Strength

The most common default. Crossed lines in two directions. Good compression strength in the XY plane. Fast to print, compatible with all materials. Best general-purpose choice when you don't have a specific reason to use something else.

Lines

Fastest Visual Only

Parallel lines in one direction only. Extremely fast. Very weak perpendicular to the lines. Only appropriate for visual/display prints where structural integrity doesn't matter. Don't use for functional parts.

Gyroid

Medium Speed 3D Strength Flexible-Friendly

A mathematically continuous 3D surface with near-isotropic (equal in all directions) strength. The best infill for parts stressed from unknown or multiple directions. Excellent in flexible materials like TPU. Slightly slower than grid but significantly more versatile. SpoolHound's general recommendation for functional parts.

Honeycomb

Medium Speed Compression

Hexagonal cells. Excellent compression resistance in the Z axis, good material efficiency. Better than grid for lightweight structural prints. Slightly harder for slicer to generate cleanly at odd angles.

Lightning

Fastest Visual Only

Branching tree-like structure that only supports top surfaces - no structural value at all. Fastest possible infill for visual prints. Do not use for anything functional.

Cubic

Slow 3D Strength

3D diagonal cubes. Good isotropic strength similar to Gyroid. Slightly more material use. A reasonable alternative to Gyroid for rigid materials.

Triangles

Medium Speed XY Shear

Triangular mesh. Good resistance to shear forces in the XY plane. Stiffer than grid in some orientations. Good for flat mechanical parts that experience in-plane loads.

Concentric

Medium Speed Flexible-Friendly

Rings that follow the perimeter inward. Maintains uniform flexibility across the print - essential for TPU and flexible filament prints. Also produces good top surfaces for visual prints.

Octet

Slow Compression

Truss-like 3D structure. Excellent compression strength per gram of material. Slow to print. Best for engineering parts needing maximum compression resistance, like press-fit inserts or structural brackets.

Rectilinear

Fast XY Strength

Parallel lines that alternate direction 90° each layer. The default in PrusaSlicer and OrcaSlicer, and the only pattern recommended for 100% infill. Faster than Grid because each layer is single-direction. Good XY strength but weaker than Grid since lines don't cross within a layer.

Adaptive Cubic

Fast 3D Strength

A smarter version of Cubic that automatically increases density near walls and top surfaces, and reduces it in the center. Same 3D strength properties as Cubic but uses significantly less material and prints faster. Available in PrusaSlicer, OrcaSlicer, and Bambu Studio. A strong choice when you want isotropic strength without wasting filament on unnecessary interior density.

3D Honeycomb

Slow 3D Strength

Like regular Honeycomb but the cell thickness varies along the Z axis, creating columns that periodically get wider and narrower. This interlocks layers vertically, giving much better Z-axis strength than flat Honeycomb. Slower to print and uses slightly more material. Best for parts that need compression resistance from all directions, not just the XY plane.

Cross

Medium Speed Flexible-Friendly

A space-filling cross-shaped fractal pattern. Designed specifically for flexible filaments like TPU - the cross pattern lets the part compress uniformly without rigid crossing lines fighting the flex. Also available as "Cross 3D" which varies density along Z. Found in Cura and OrcaSlicer. An alternative to Concentric when you need uniform squishiness rather than ring-based flex.

Decision Guide

Use Case	Recommended Pattern	Percentage	Notes
Visual / decorative	Lightning or Lines	10-15%	Print time priority; no structural need
Functional, unknown stress direction	Gyroid or Adaptive Cubic	20-30%	Best all-rounders; Adaptive Cubic saves material in large parts
Flat part, in-plane loads	Triangles or Grid	25-40%	Good shear and XY compression
Part under compression	3D Honeycomb or Octet	30-50%	Z-axis compression resistance; 3D Honeycomb stronger than flat
TPU or flexible part	Concentric, Cross, or Gyroid	15-25%	Cross for uniform squish; Concentric for ring-based flex
Maximum strength	More walls + Gyroid	40%+	5+ walls often beats higher infill; combine both
100% solid infill	Rectilinear	100%	Only pattern recommended for solid parts; slicers auto-switch to it
Speed priority	Lightning or Lines	10%	Accepts visual quality tradeoff

When in doubt, use Gyroid at 20%. It's the most forgiving choice for functional prints and handles unexpected load directions well.

For TPU specifically: Concentric infill maintains uniform flexibility across the part. Gyroid also works well. Avoid Grid or Lines in flexible filaments - the rigid crossing pattern fights the material's natural flex.

Why Infill Percentage Affects Top Surfaces

Too-low infill causes pillowing - the top surface sags or bridges poorly between infill contact points, producing a rough, uneven top. The fix is either more infill, more top layers (3 minimum, 4-5 recommended), or enabling ironing in your slicer.

Minimum top layers: 3 at 0.2mm layer height (0.6mm total). For smooth tops, use 4-5 layers or enable ironing.

Pattern choice matters: Grid and Honeycomb support top surfaces more uniformly than Lines at the same percentage. Lightning provides almost no top surface support - compensate with extra top layers.

Ironing (a slow extra pass over the top surface at reduced flow) dramatically improves top surface finish at the cost of print time. Worth enabling for visual parts.

Common Infill Mistakes

Raising infill instead of adding walls. A 4-wall print at 20% infill is almost always stronger than a 2-wall print at 60% infill. Walls are load-bearing; infill mainly supports top surfaces.

Using Lightning infill on functional parts. Lightning infill has no structural value - it only prevents top surface sag. It looks identical to other patterns on the outside.

Not adjusting top layers for low infill. At 10% infill, use 5+ top layers or you'll get pillowing regardless of pattern.

Printing TPU with Grid infill. The rigid crossing pattern fights TPU's natural flex. Use Concentric or Gyroid for all flexible filament prints.

Assuming higher infill = waterproof. Watertightness comes from wall count and material choice, not infill density.

Browse Filament on SpoolHound Wall Thickness Guide →