15% vs 30% infill: strength, print time and filament
Infill is the sparse structure inside a part. The percentage says how much of the core becomes plastic: 15% is an open lattice, 100% is a solid part. The outside doesn't change: walls, top and bottom stay solid.
Where a part's strength comes from
A 3D print is a solid shell around a sparse core. What resists bending, twisting and impact is mostly the shell: the walls (perimeters) and the top and bottom layers. Prusa says it plainly (checked November 2026): a model's strength is mostly defined by the number of perimeters, not the infill, which helps more with compression resistance and stiffness.
That is why Bambu Lab's own 0.20mm Strength profile, built for stronger parts, raises walls from 2 to 6 and infill only from 15% to 25%.
What each percentage costs
| Infill | Filament | Time | What it's for |
|---|---|---|---|
| 0% (shell only) | 10.7 g | 17 min | Almost never: the top has nothing under it |
| 10% | 19.0 g | 20 min | Decorative parts and large parts that just sit there |
| 15% (Bambu Studio default) | 22.9 g | 23 min | Most parts |
| 20% | 26.9 g | 26 min | A bit more stiffness |
| 30% | 34.4 g | 31 min | Parts with clamping, screws or loads |
| 50% | 50.4 g | 45 min | Parts that get compressed |
| 100% | 89.2 g | 1 h 23 min | Rare: maximum weight and stiffness |
| 15% with 4 walls | 27.7 g | 27 min | Functional parts without paying for 30% |
Illustrative example: a solid 60 × 40 × 30 mm block, Grid pattern, 2 walls (except the last row), 5 top and 3 bottom layers. Estimated by OrcaSlicer 2.4.2 with the Bambu Lab X1 Carbon 0.20mm Standard profile (0.4 mm nozzle) and PLA Basic. A slicer prediction, not a measurement: different parts respond differently.
Three things stand out:
- The shell is almost half the weight. Its 10.7 g are 47% of the part at 15%. That is why doubling infill doesn't double weight: from 15% to 30%, filament went up 50% and time 37%.
- 4 walls cost less than 30%. They came out at 27.7 g and 27 minutes, against 34.4 g and 31 minutes, and they reinforce the part of the print that does the most work.
- 100% is expensive. Almost 4 times the filament of 15%.
In money, the extra 11.5 g at 30% cost about $0.23 per part at $0.02 a gram. On a batch of 20 parts, that is 230 g ($4.60) and almost 3 more hours of printer time. The material math is in the guide to cost per gram.
Which pattern to choose
| Pattern | Filament at 15% | Time at 15% | Good for |
|---|---|---|---|
| Grid | 22.9 g | 23 min | General use; lines cross within the same layer |
| Cubic | 23.1 g | 23 min | Similar strength in every direction |
| Gyroid | 22.9 g | 44 min | Every direction plus a little flexibility |
| Honeycomb | 26.5 g | 43 min | Strong, but uses more and prints slowly |
| Adaptive Cubic | 20.0 g | 20 min | Large parts: dense near the shell, sparse in the middle |
| Lightning | 12.4 g | 19 min | Just holding up the top of decorative parts |
Same block and profile as the table above, at 15% with 2 walls. Strength notes follow the tables in the OrcaSlicer wiki and from Prusa (checked November 2026).
Gyroid used the same plastic as grid and almost twice the time in this estimate: the curves force the printer to slow down. It pays off on parts loaded from several directions, not as a default for everything. Lightning is great for decorations and poor for functional parts, because it leaves most of the core empty.
Which value for which part
- Decorations, vases, figures: 10% to 15%, or Lightning if it only needs to hold up the top.
- General use (organizers, desk stands, boxes): 15% to 20% with 2 or 3 walls.
- Functional parts with screws, snap fits or loads: raise walls to 3 or 4 first, then infill to 25% to 30%.
- Spacers, feet and parts that get squeezed: this is where going above 30% is worth it, because the core is what resists compression.
Where it is in the slicer
- Bambu Studio and OrcaSlicer: the Strength tab. In the Sparse infill group (Infill in OrcaSlicer): Sparse infill density and Sparse infill pattern. Walls are under Walls > Wall loops, and top and bottom under Top/bottom shells. With Bambu profiles in OrcaSlicer, the pattern may default to Cross Hatch instead of Grid.
- PrusaSlicer: Print Settings > Infill > Fill density and Fill pattern; walls are under Layers and perimeters > Perimeters.
- Cura: the Infill section, Infill Density and Infill Pattern; walls are under Walls > Wall Line Count.
Common mistakes
- Raising infill to fix a weak part that has 2 walls. Walls first.
- Assuming 100% is always better. In the example it was almost 4 times the material and more than 3 times the time, and Prusa warns it can hurt the look of the part.
- Switching patterns without checking time. In the estimate, gyroid doubled the block's print time.
- Low infill with few top layers. The top sags between the infill lines. Keep about 1 mm of top, like Bambu's default profile (5 layers of 0.2 mm).
Frequently asked questions
Does a part at 15% infill weigh 15% of a solid one?
No. The shell is always solid. In the example block, 15% weighed 22.9 g, or 26% of the 89.2 g solid version. The smaller and thinner the part, the larger the shell's share of the weight.
Can I use more infill in just one area?
Yes. In Bambu Studio and OrcaSlicer, add a modifier over the area, such as around a screw hole, and change the density only there. PrusaSlicer has modifiers too, and Cura does the same with Per Model Settings.
Can infill show through the outside?
It can. With only 2 walls and a light or translucent filament, the infill pattern sometimes shows through the wall against the light. One more wall usually fixes it.
Does the pattern change the weight?
Not much at the same percentage: grid, cubic and gyroid all came out near 23 g in the example. What changes a lot is time. Honeycomb uses more and Lightning much less, because it doesn't fill the whole core.
Does layer height change infill time too?
Yes. Thinner layers multiply the passes through the whole core. The effect is covered in the guide to layer height.