GLOSSARY
Infill
Infill is the partially-hollow internal structure of a 3D print. Instead of solid plastic, the slicer fills the inside with a sparse pattern — saving time, weight, and material.
Definition
A 3D printed part has three regions: the outer walls (perimeters), the top and bottom solid layers, and everything in between, which is the infill. You set a density (typically 10–30%) and a pattern (gyroid, grid, cubic, honeycomb, lightning) and the slicer generates the corresponding internal lattice.
Why it matters
Infill is the strongest cost-vs-strength lever in slicing. 100% infill is almost never necessary — most of a part's strength comes from the wall count, not the inside. 15–20% gyroid infill is plenty for visual prints; 30–40% for functional ones; 60%+ only for heavily loaded mechanical parts.
Pattern matters less than density for most users. Gyroid is a good default — isotropic, fast, pleasing to look at when peeking inside. Grid is fast but anisotropic. Lightning infill (Cura, PrusaSlicer) uses minimal material to support the top layers and almost nothing else; great for visual prints where strength is irrelevant.
Common confusion
Doubling infill density does not double strength. Beyond about 40%, adding more infill barely improves part stiffness — increase wall thickness instead. Two extra perimeters do more than 20% extra infill.