Infill and Layer Height
Infill is the internal structure printed inside an FDM part, and layer height is the thickness of each printed layer. Together they set much of a print's weight, surface, and print time, but walls and orientation usually matter more for strength.
Updated 28 Sep 2026 · 5 min read · By Wyntek
What infill and layer height are
An FDM part is rarely printed solid. The slicer prints the walls, called perimeters, and the top and bottom skins solid, then fills the inside with a sparse internal structure called infill. Infill percentage is how much of that inside volume is filled: 0% is hollow and 100% is solid.
Layer height is the thickness of each layer the printer lays down. It sets how finely curves and slopes are stepped, and it has a large effect on print time. Both are print settings, not features of the CAD model, so the same file can be printed light and fast or dense and fine.
How much infill
Infill's main job is to hold up the top surfaces, which would otherwise have to bridge across empty space. Prusa's testing found 10 to 20% to be the best balance of strength, reliability, print time, and material, and it uses that range in its PrusaSlicer profiles. It also notes that setting infill above 40% rarely makes sense.
More infill does make a part tougher, but walls do more of the work. Prusa states that a model's strength is mostly defined by the number of perimeters, not the infill, and that the extra toughness from infill above 20% can be had by adding perimeters instead. In most cases a solid part is no stronger in use than one with sparser infill, and it costs far more material and time.
Infill patterns
| Pattern | Structure | Notes |
|---|---|---|
| Rectilinear | Lines in one direction, turned 90 degrees on the next layer | One of the fastest patterns, and the one used for 100% infill |
| Grid | Lines in both directions on every layer | Simple and fast, but material builds up where lines cross |
| Cubic | Stacked cubes standing on one corner | Leaves many air pockets inside the part |
| Gyroid | A smooth, wavy 3D surface | Supports well in every direction, prints relatively fast, and saves material |
| Honeycomb | Hexagonal cells | Strong, but uses about 25% more material and can take up to twice as long |
| Adaptive cubic | Dense near the walls, sparse in the middle | Uses about a quarter less material than rectilinear |
| Support cubic | Density rises only toward the top surfaces | Lowest material use and print time; holds up the top but adds no strength |
For a functional part with no special needs, gyroid is a sound default: Prusa calls it one of the best infills because it supports the part in every direction. For display models, a top-supporting pattern such as support cubic saves the most time and material.
Layer height: detail, time, and strength
On a standard 0.4 mm nozzle, common layer heights run from about 0.1 to 0.3 mm. Prusa's rule is to keep layer height below 80% of the nozzle diameter, which caps a 0.4 mm nozzle at about 0.32 mm. It advises against going below 0.10 mm, because thinner layers add a lot of time for little visible gain.
Print time is roughly inversely proportional to layer height: halving the layer height about doubles the number of layers and the time. Surface detail moves the other way. Thinner layers show less stepping on curves and shallow slopes, where each layer steps out from the one below. Vertical walls change less.
Layer height also changes strength across the layers. In CNC Kitchen's tests of PLA printed with a 0.4 mm nozzle, layers from 0.05 to 0.2 mm bonded best, with 0.15 mm the strongest, while 0.3 mm layers carried only about half the load and 0.4 mm layers held almost nothing. For strong parts, keep layers at or below half the nozzle diameter.
| Layer height | Surface | Print time | Strength across layers |
|---|---|---|---|
| 0.1 mm (0.004 in) | Fine, least visible stepping | About twice as long as 0.2 mm | Good |
| 0.2 mm (0.008 in) | Standard | Baseline | Good, and a sound default for strength |
| 0.3 mm (0.012 in) | Coarse, visible layers | About two thirds of 0.2 mm | About half in one test, so avoid it for loaded parts |
What to change first for a stronger part
- Add perimeters. Walls carry most of the load, and extra perimeters add more strength than extra infill.
- Orient the part so the load runs along the layers. In CNC Kitchen's tests, hooks loaded across the layers failed at loads at least 50% lower than the same hooks loaded along them.
- Keep layer height at or below half the nozzle diameter, which is 0.2 mm on a 0.4 mm nozzle.
- Add top and bottom layers if the skins are thin. Thinner layers need more of them for the same skin thickness: Prusa's example uses 3 top layers at 0.3 mm but 9 at 0.1 mm.
- Raise infill last. Above 20% a part gets tougher, but beyond 40% the gain rarely justifies the time and material.
At Wyntek
When you order an FDM part from Wyntek, you choose the material, layer height, infill, and supports in the job flow. Upload your file and you see the price in US dollars before you submit. Every part is scanned and inspected before it ships.
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