Infill is the internal structure of a 3D print - the lattice of plastic inside solid-looking parts. Choosing the right infill pattern and percentage has a bigger impact on strength, weight, and print time than most beginners realise.
When your slicer processes a model, it creates:
The infill percentage controls how densely packed this internal structure is. 0% infill = completely hollow (fragile). 100% infill = completely solid (strong but heavy and slow).
Most prints don't need 100% infill. A 20% infill with the right pattern is surprisingly strong.
| Percentage | Strength | Use Case |
|---|---|---|
| 0% | Very weak | Display models, decorative items you won't handle |
| 5-10% | Weak | Lightweight decorative items |
| 15-20% | Moderate | General household objects, display pieces |
| 25-40% | Good | Functional parts with moderate loads |
| 50-60% | Strong | Load-bearing parts, brackets, clips |
| 80-100% | Very strong | Maximum strength parts, impact-absorbing pieces |
Default starting point: 15-20% for decorative items, 40% for functional parts. You rarely need more than 40% unless the part will be under significant stress.
The simplest pattern - two sets of lines crossing at 90 degrees. Fast to print and reasonably strong in the XY plane.
Best for: General use, fast printing. The default in most slicers.
A complex three-dimensional wave pattern. Strong in all directions, good for flexible materials, and has an unusual aesthetic when visible through walls.
Best for: Parts that need strength in multiple directions, especially those under torsion or multi-axis loads. Popular choice for functional parts.
Hexagonal cells, similar to natural honeycomb structure. Excellent strength-to-weight ratio, though slower to print than grid.
Best for: Lightweight structural parts where strength matters.
A 3D version of honeycomb with diagonal bracing in all three planes. Very strong in all directions.
Best for: Parts under compression or multi-directional loading.
Follows the outline of the model inward in concentric rings. Weak structurally but produces beautiful top surfaces and is excellent for flexible prints.
Best for: Flexible parts (TPU), artistic pieces where top surface matters.
Minimal internal structure that just supports the top layers - not a traditional infill pattern. Produces the lightest prints possible.
Best for: Display items and decorative pieces where weight and material savings matter. Not suitable for functional parts.
Lines printed in a single direction per layer. Very fast, less strong than grid in one axis.
Best for: Fast drafts and prototypes.
Increasing infill from 15% to 40% roughly doubles print time for the infill layers, but doesn't double strength. The majority of a part's strength comes from:
For maximum strength with minimal print time increase: increase wall count to 4-5 before increasing infill beyond 30%. This is often more effective.
Most slicers have an "infill overlap" setting - how much the infill overlaps with the inner wall. A value of 20-25% is typical and ensures good bonding between infill and walls.
If you're seeing separation between infill and walls, increase infill overlap slightly.
If your top layers look bumpy or you can see the infill pattern through them, you need more top layers. Most slicers default to 3-4 top layers - increase to 5-6 for a smoother top surface, especially at low infill percentages.
Most of the time, changing the infill pattern matters less than the percentage and wall count. Gyroid is a solid default for anything functional - it's strong in all directions and the extra print time is minimal.