What Infill Percentage Should You Use?

20% is the number almost every slicer ships with, and for a general-purpose part it’s a perfectly good answer. It is the wrong answer often enough, in both directions, that it’s worth five minutes to understand what the dial actually does.

The Short Answer

Notice how much of the table sits under 25%. The useful range is narrower than the slider suggests.

Walls Beat Infill

This is the single most useful thing to know about infill, and it saves more filament than any other setting change.

A 3D-printed part is closer to a hollow box than a solid block. Under bending and impact, the load travels through the outer shell. The infill mostly stops the shell from collapsing inward. So adding perimeters puts material exactly where the stress is, while adding infill puts material where it mostly rides along.

In practice: three walls at 20% infill will usually outperform two walls at 50% infill, and it prints faster and uses less filament. If a part broke, add a perimeter before you touch the infill slider. Top and bottom layers matter for the same reason. Four or five solid layers on each face stiffens a flat part far more than doubling the density underneath.

Miniatures and Display Prints

Small, detailed models are almost all shell. Once the walls and the top and bottom layers are printed, there is barely any interior left for infill to occupy, so 10% and 25% produce nearly identical parts at meaningfully different print times.

For anything under about 60mm, start at 10%. For hollow busts and props printed as thin shells, 5% with a lightning or gyroid pattern is plenty; the infill exists only to support the top surfaces.

The exception is a miniature you want weighted for tabletop feel. There, print at low infill and add the weight afterward with a slug or shot in a cavity. It’s cheaper than filling it with plastic.

Functional and Load-Bearing Parts

Here the density genuinely matters, but so does the direction of the load, which is where the pattern comes in.

• 25-40% covers most brackets, mounts, and enclosures. Combine with three or four walls.
• 40-60% for parts under real mechanical stress: gears, motor mounts, arms that carry weight.
• Above 60%, returns fall off sharply. You are paying a lot of filament and time for a few percent of stiffness.

The bigger lever for functional parts is orientation. A part printed so the load runs across layer lines rather than along them can be several times stronger at the same infill, because layer adhesion is the weakest axis in FDM. Rotate the model before you raise the density.

When 100% Actually Makes Sense

Rarely, and it has real costs.

Solid infill traps heat, so large solid parts warp more, especially in ABS and ASA. It also takes a long time and can over-extrude on the top surfaces where the slicer packs lines tightly together. And because the outer shell already carries most of the load, going from 60% to 100% often buys less strength than adding two perimeters would have.

Use it selectively instead. Every modern slicer supports a modifier or per-region setting, so you can make a bolt boss or a threaded insert area solid while leaving the rest of the part at 20%. That is almost always the better answer than a globally solid part.

What Density Costs

Rough numbers for a midsize functional part at 0.2mm layers with three walls. Your model will vary, but the shape of the curve holds:

• 10% to 20% - noticeably stiffer, modest time and filament cost. Worth it.
• 20% to 40% - real stiffness gain, roughly 25-40% more time. Worth it for functional parts.
• 40% to 60% - smaller gain for a similar cost. Justified only under load.
• 60% to 100% - large cost, small gain. Almost never worth it globally.

The nonlinearity is the point. Past roughly 50%, the walls and solid top and bottom layers are carrying the part, and extra lattice mostly adds mass.

Pattern Changes What a Percentage Means

20% gyroid and 20% lines use similar amounts of plastic and behave completely differently. Gyroid supports in every direction, lines are strong along one axis and weak across it, honeycomb is stiff in plane, and lightning barely resists anything but holds up the top surface.

So “what infill percentage” and “which infill pattern” are one question, not two. Pick the pattern for how the part is loaded, then pick the density for how hard.

A Rule You Can Repeat

Start at 15-20% with a gyroid or grid pattern and three walls. If the part fails, ask what broke:

• Snapped along a layer line - reorient the part, then raise the temperature slightly.
• Crushed or dented inward - raise infill.
• Flexed too much across a flat span - add top and bottom layers.
• Cracked at a thin section - add perimeters, not infill.

Log which combination you used and what happened. Two or three logged prints of the same bracket will teach you more about your machine than any recommended table, this one included.