3D Printing Infill: Patterns, Percentages, and the Gyroid

Infill is the internal lattice your slicer prints inside the walls of a part. The shell gives you the surface; the infill gives the part its body without filling it solid. You set it as a density percentage, and the pattern you pick matters as much as the number.

What the Percentage Means

0% is hollow, 100% is solid plastic. Almost nothing needs to be solid, and almost nothing should be fully hollow, so the useful range lives in between.

That percentage isn’t a fill-by-volume number you can eyeball. At 20%, the slicer spaces the lattice so roughly a fifth of the interior is plastic. The pattern decides how those lines are arranged, and the arrangement changes how the part behaves under load.

How Density Trades Off

Every point of infill you add costs filament and time and buys you weight and stiffness. The relationship is not linear, and the back half of the dial is mostly wasted.

• 10-15% - Display pieces, busts, cosplay props, prototypes you just want to look at. A bust at 10% prints in a fraction of the time and grams of one at 40%, and you’ll never feel the difference on a shelf.
• 20-40% - The functional default. Brackets, enclosures, jigs, toys, most household parts. 20% handles general use; push toward 40% for parts that get handled hard or carry moderate load.
• 50%+ - Real mechanical load: gears, motor mounts, tool bodies, anything bolted down and stressed. Above 50% you pay a lot of plastic for shrinking returns.

Here’s the part people miss. Going from 20% to 40% adds real stiffness. Going from 60% to 80% adds plastic and print time for almost nothing, because past a point the walls and the top and bottom layers carry the load, not the lattice.

So if a part feels weak, add a perimeter before you crank infill. Three walls at 20% will usually beat two walls at 50%, and it prints faster too. For cost, a rough feel: at 0.2mm layers on a midsize part, jumping from 15% to 50% can double print time and filament. Set the dial for what the part does, not for “more is safer.”

The Patterns Worth Knowing

Slicers ship a dozen patterns. These five cover almost everything.

• Grid - Straight lines crossing in two directions, layer over layer. Fast, simple, decent in most directions. The catch: crossing lines stack at the same points, and the nozzle ploughs over those intersections, which can tick or knock at high speeds.
• Lines / Rectilinear - Parallel lines that alternate direction each layer. Fastest and lightest, but weak in-plane. Fine for low-density display work, not for load.
• Triangles - Strong in the plane of the layer, good for parts stressed sideways. Heavier and slower than grid at the same density.
• Honeycomb - Hexagonal cells. Strong in several directions and great-looking through a translucent print, but slower, because the path has more direction changes and retractions.
• Gyroid - A continuous 3D wave. More below, since it’s the one this app is named after.

Why the Gyroid Earns the Spotlight

A gyroid is a single curved surface that repeats along all three axes, so the lattice has no flat planes and no stacked intersections. That geometry buys you a few things at once.

Near-isotropic strength. Most patterns are strong in one or two directions and weak in the rest. The gyroid is close to equally strong in every direction, so you don’t have to predict how a part will be loaded and orient your infill to match. For oddly stressed parts, that’s one less thing to get wrong.

It prints fast and quiet. Within a layer, the toolpath is one smooth, continuous curve. No crossing points to plough over, few or no retractions, no sharp corners forcing the printer to decelerate. The result holds speed and runs noticeably quieter than grid at the same density. The nozzle isn’t slamming direction every few millimeters.

It plays well with flexibles. TPU hates retractions, which cause stringing and jams. The gyroid’s near-retraction-free path makes it one of the better choices for flexible filament, where grid and honeycomb fight you.

The tradeoff is small. The curved path can be marginally slower than plain lines at very low density, and it uses a touch more filament than rectilinear for the same percent. For anything functional, the strength-per-gram and print quality pay for it.

Practical Recommendations

• General parts: gyroid at 15-20%. Best all-rounder and a sane starting point.
• Display only: lines or gyroid at 10-15%. Don’t overthink it.
• Real load: gyroid or triangles at 30-50%, and add walls before you add density.
• Flexible filament: gyroid, low density, to keep retractions down.
• Translucent showpiece: honeycomb at 15-20% looks sharp through the wall.

Pick the pattern for how the part is stressed and the density for how hard, then leave the rest of the dial alone. If you remember one setting, make it gyroid at 20% with three walls. That covers a surprising amount of real printing, and you can log the exceptions as you hit them.