Infill vs walls: what makes a 3D printed part stronger?
For many functional FDM parts, additional walls or perimeters provide more useful strength than extremely high infill. The outside of a part carries much of the stress under bending, while infill mainly supports the shell, top layers and compression loads. Prusa also notes that model strength is largely determined by the number of perimeters rather than infill alone.
What does infill actually do?
Infill can help in several ways. But 100% infill does not automatically mean the best functional part.
- support top surfaces
- connect opposite walls
- increase stiffness
- help under compression
- influence print time and material use
Why walls matter
Under bending, high tensile and compressive stresses often occur near the outer surfaces. Increasing wall thickness adds material exactly where it can be mechanically useful. Especially relevant for:
- hooks
- brackets
- mounts
- handles
- tabs
When does more infill help?
Higher infill can still be useful for:
- compression loads
- local screw areas
- local load concentration
- supporting large top surfaces
- increasing overall stiffness
There is no universal infill percentage
Do not claim that 20% is always enough or that 50% is strong. Geometry and load case matter.
Practical workflow
- understand the load direction
- choose enough walls
- use sensible infill
- check print orientation
- test highly loaded parts