Infill

Infill is the internal lattice structure a slicer builds inside a model, between the solid outer walls, rather than printing the inside completely solid. Most functional parts do not need to be full plastic all the way through, so infill exists to add internal strength and rigidity without using anywhere near the material or time a fully solid print would need.

Two settings control infill: density, expressed as a percentage of how much of the interior is filled, and pattern, the shape the internal structure repeats in. Low density around 10 to 15 percent suits decorative prints, moderate density around 20 to 30 percent covers most functional parts, and higher density suits parts that need to resist real load or repeated stress.

Pattern choice matters too. Grid and honeycomb patterns are common all-purpose choices, while patterns built for strength in one direction suit parts that mostly bend or flex one way. A frequent beginner mistake is printing everything at high infill by default, which wastes filament and print time on parts, like a simple decorative box, that never needed that much internal material in the first place.