HOW TO CHOOSE INFILL PATTERN AND DENSITY

Infill is the structure inside the walls of a print. Solid infill (100%) maximises strength but also maximises print time and material. 0% infill is hollow - prints fast and light but is fragile. The sweet spot for most prints is 15-25% with a pattern matched to the use case. Pattern matters as much as density. Lightning infill is just enough material to support the top layer - fastest possible print. Gyroid is a 3D triangle pattern that provides equal strength in all directions. Grid is fast to slice but weak under torsion. Choose based on what the part will actually do.

Use low density (5-15%) for: display pieces, decorative items, prototypes, parts that need to be lightweight (cosplay armour). Use medium density (20-30%) for: general-purpose prints, hobby parts, parts that need some structure but aren't load-bearing. Use high density (40-60%) for: functional parts, mechanical components, parts under stress. Use solid (100%) for: thin parts where infill won't fit (anything under 4-5 mm thick), parts where every bit of strength matters. Don't use 100% by default. It triples or quadruples print time and rarely adds proportional strength. For most prints 20% gyroid is structurally fine and 5x faster.

Pattern selection: - Gyroid: best strength-to-weight ratio. Equal strength in all directions. Slightly slower to slice. Use for: functional parts, anywhere strength matters. - Cubic / Cubic Subdivision: fast to slice, good strength in all axes. Use for: general-purpose prints. - Grid: fastest to slice, fast to print. Weak under torsion (twisting). Use for: simple decorative prints. - Lines / Rectilinear: simplest, fast slice. Same weakness as Grid. Use for: drafts. - Lightning: least material possible. Just enough to support top layer. Use for: display pieces with no structural requirements. - Triangles: strong in 2D, prints fast. Use for: flat decorative parts. - Honeycomb / Hexagonal: strong-to-weight in compression. Use for: parts with vertical loads. - Concentric: follows model outline. Used mostly for top/bottom layers; rare as primary infill. Density selection by use case: - 0%: vases, hollow shells (Vase Mode). - 5-10%: lightning infill / decorative. - 15%: standard hobby prints, figurines. - 20%: general-purpose default. - 25-30%: stronger general parts. - 40-50%: functional parts under load. - 60-80%: mechanical parts, brackets, fixtures. - 100%: thin walls, maximum-strength parts. Slicer-specific notes: - Cura: Infill - Pattern + Density. - PrusaSlicer: Infill - Fill density + Fill pattern. - OrcaSlicer / Bambu Studio: Strength - Sparse infill density + pattern. Wall and top/bottom layer combo: - 3 walls + 5 top/bottom layers + 20% gyroid is a strong default. - For lighter prints: 2 walls + 4 top/bottom + 10% lightning. - For functional: 4 walls + 6 top/bottom + 30-40% gyroid.

100% infill on everything. Wastes 5-10x the print time of 20% infill for marginal strength gain. Use 100% only when you need it. Lightning infill on functional parts. Lightning is *just* enough to support the top layer. Tap the print and it crumbles. Use only for display. Forgetting infill direction matters. Grid has weak torsional strength. A gear or shaft printed with grid infill twists apart under torque. Use gyroid or cubic. Grid infill on tall thin walls. The infill can't connect across thin features and provides no support. Switch pattern or increase wall count. Setting density without considering walls. 4 walls + 0% infill is often stronger than 2 walls + 30% infill. Walls add strength faster than infill density.

For layer height paired with infill for strength, see how-to-choose-layer-height. For top surface quality paired with infill density (low density = pillowing risk), see rough-top-surface. For under-extrusion that looks like infill failures, see under-extrusion.