Is it better to increase walls or infill for strength?

Walls, in most cases. The outer skin carries the bending and crushing load, so an extra perimeter adds more strength per gram than extra infill does.

What infill percentage is strong enough?

Most parts are fine at 10–25%. Slant 3D tested every pattern at 25%. If a section needs more, add walls or make it solid instead of creeping infill up.

Does 100% infill make a 3D print strongest?

A solid section is the strongest option, and printing handles it without the shrink problems of molding. It costs the most time and plastic, so use it only where the part needs it.

Does infill pattern affect strength?

Less than people think. At the same density, Slant 3D found the pattern mostly changes how a part fails, and grid or triangles is the reliable default.

3D Printing3D Modeling / DFMWalls vs. infill

Walls vs. infill: which makes a 3D print stronger?

The part snapped. So you reprint it at 80% infill, wait twice as long, and it snaps in the same spot. Walls vs. infill is the first strength question in 3D printing, and the answer is almost always walls. The outer skin carries the load. Infill mostly holds the skin in shape.

⚡ Rule of thumb

Add perimeters (walls) before you raise infill; keep infill at 10–25% grid or triangles as the baseline, and if a section truly needs to be strong, model it solid.

Starting point

Infill 10–25% grid / triangles · add walls first · solid where it really counts

Measured

Infill density (%) and perimeter (wall) count

Confidence

Widely accepted

▶ Source video — Learn How Infill Patterns Behave Under Stress — Slant 3Dwatch on YouTube ↗

Applies to

Process: FDM / filament
When: Tuning a part for strength or stiffness
Default: Grid or triangle infill, 10–25%
Goal: Strength on the load path, not wasted plastic

Why it matters

3D printing has a superpower. A part can be hollow without being hollow. The infill inside is a light cross-hatch that gives the part structure without much weight, which is why Slant 3D says most parts run 10–25%.

But most of the strength is in the outer skin. Pouring on infill adds plastic in the middle, where bending and crushing loads barely reach. An extra perimeter puts that plastic right on the load path.

And when a part really has to be strong? Make it solid. Printing doesn’t suffer the shrinkage that makes thick sections a problem in molding, so a solid section is a real option, not a defect.

What good looks like

Load-bearing areas get extra perimeters, not just denser infill
Infill sits at 10–25% grid or triangles unless there’s a reason to change
If it truly needs to be solid, it’s modeled or sliced solid
Pattern changes are made on purpose, for a specific failure mode

How to apply it

Find where the part actually carries load: the bending root, the screw boss, the clip.
Add perimeters there first. Three to four walls is a good working range.
Leave infill at 10–25% grid or triangles as your baseline.
If it still fails, make that section solid rather than maxing infill everywhere.
Only switch infill patterns when you care how the part breaks (crush vs. snap).

Test it on your setup

Print the same part twice: once with 2 walls at 50% infill, once with 4 walls at 20%. Weigh them, then break them the way the part gets loaded. Compare print time, weight and where it cracked.

Exceptions & tradeoffs

Mind you, infill isn’t useless. It braces the top skin so it doesn’t sag, and it stops thin walls buckling under a squeeze. Drop it too low and the top surface droops between the lines.

For a defined engineering requirement, like energy absorption or a controlled break point, the infill pattern genuinely matters. Pick it for the failure behaviour you want.

Common mistakes

Cranking infill to 80–100% to make a weak wall strongAdd perimeters; walls carry the load far more efficiently
Chasing the ‘strongest’ infill patternAt equal density the pattern mostly changes how it breaks; grid or triangles is the reliable default
Setting 100% infill in the slicer and calling it solidFine for a test, but model the section solid if the design depends on it

Frequently asked questions

Is it better to increase walls or infill for strength?Walls, in most cases. The outer skin carries the bending and crushing load, so an extra perimeter adds more strength per gram than extra infill does.
What infill percentage is strong enough?Most parts are fine at 10–25%. Slant 3D tested every pattern at 25%. If a section needs more, add walls or make it solid instead of creeping infill up.
Does 100% infill make a 3D print strongest?A solid section is the strongest option, and printing handles it without the shrink problems of molding. It costs the most time and plastic, so use it only where the part needs it.
Does infill pattern affect strength?Less than people think. At the same density, Slant 3D found the pattern mostly changes how a part fails, and grid or triangles is the reliable default.

Slant 3DSource & visual reference

Infill gives structure without weight; most parts run 10–25%; strength is in the outer skin; solid is an option without shrinkage worries — Learn How Infill Patterns Behave Under Stress | 3D Printing Experiment ↗ at 00:00.