Infill: which percentage to choose, and why 100 % is nearly always a mistake
What infill actually does, why raising it adds almost no strength past 30 %, and which percentage to ask for by type of part.
A printed part is hollow inside. The outer walls are solid, and the interior is filled with a lattice that gives it body. The infill percentage says how much of that lattice there is: at 15 % the inside is mostly air; at 100 % it is solid plastic.
The diminishing returns
This is the point that changes how you order: strength does not rise in a straight line with infill. From 10 % to 30 % the difference is large. From 30 % to 60 % it is much smaller. From 60 % to 100 % it is barely noticeable — but the price is, because material and machine time do rise in a straight line.
What to ask for, by type of part
| Type of part | Infill | Reason |
|---|---|---|
| Model, figure, decorative piece | 10 – 15 % | It only has to hold itself up. |
| Enclosure, box, everyday part | 15 – 20 % | The standard. Covers nearly everything ordered. |
| Bracket, tool, working part | 25 – 40 % | Where infill still genuinely contributes. |
| Part to be tapped or drilled later | 50 % or locally solid | A drill into air has nothing to bite. |
| Part that must have weight or act as ballast | 100 % | The one case where solid is the point. |
What infill does not fix
- Layer separation. If the part splits along a layer, that is an orientation problem, and more infill changes nothing.
- A wall that is too thin. A 0.8 mm wall stays weak however solid the middle is.
- A sharp corner where stress concentrates. That is fixed with a fillet, not with material.
- Heat resistance. That depends on the material, not on how much of it is inside.
In the configurator, infill is an option with its price on screen: raise it and you see what it adds before ordering. For the vast majority of parts the default is right, and the money is better spent on a better material.