3D Printing Walls vs Infill: What Actually Matters
The Right Balance for Automotive Clips & Brackets
It's not just about walls or infill - it's about the right combination. Fewer walls with high infill often beats many walls with low infill.
The Key Insight
3 walls with 70-80% infill is ideal for clips that need to flex. 4+ walls for rigid brackets. 3 walls with high infill gives better dimensional accuracy and flex than 5 walls with low infill.
Walls (Perimeters)
Walls carry tensile loads (pulling forces)
Walls resist bending and flex stress
More walls = better layer adhesion at edges
Walls create solid perimeter for snap-fit features
Surface finish is determined by walls
Each wall adds ~0.4mm of solid material
Infill
Infill provides internal structure
Infill resists compression (crushing) forces
Infill supports top layers during printing
Pattern choice affects strength direction
Less infill = lighter parts, faster prints
Gyroid/honeycomb are strongest patterns
Strength Comparison
| Configuration | Tensile | Bending | For Clips | Weight |
|---|---|---|---|---|
| 2 walls, 50% infill | Weak | Poor | Fails quickly | Light |
| 3 walls, 80% infill | Good | Good | Best for flex | Medium |
| 4 walls, 70% infill | Very Good | Very Good | Less flex | Medium |
| 5 walls, 70% infill | Excellent | Excellent | Rigid | Heavy |
Key Insights
Walls Handle Bending
When a clip flexes, stress concentrates at the outer surface. But too many walls = too rigid to flex properly.
Infill Handles Compression
High infill (70-80%) distributes stress evenly and prevents internal failures. More important than wall count for durability.
3 Walls + High Infill for Clips
Fewer walls with high infill gives better flex, better dimensional accuracy (less wall overlap), and lower internal stress.
Pattern Matters
Gyroid infill has no weak direction. Grid/lines are stronger in one axis. Use gyroid for automotive parts.
Settings by Part Type
Trim Clips & Fasteners
Rigid Brackets
Heavy-Duty Mounts
Covers & Bezels
Hinges & Moving Parts
Test Fits / Prototypes
What Research Shows
Walls matter more than infill for bending/flex strength
Snapmaker Research3-5 walls is the practical sweet spot for functional parts
3DISMImpact strength peaks at 80-85% infill - 100% is too homogenous for crack resistance
Journal of Materials Research & TechnologyStrategic internal voids provide crack deflection paths, improving fracture toughness
Nature CommunicationsIncreasing perimeter layers improves stress distribution - returns diminish after 3 walls
Frontiers in Mechanical Engineering
Frequently Asked Questions
Why do my clips keep breaking at the base?
Could be too few walls OR too many. With 2 walls there's not enough material. With 5+ walls the part is too rigid and cracks instead of flexing. Try 3 walls with 80% infill - gives flex where you need it.
Is 100% infill ever worth it?
Rarely. Peer-reviewed research (Mishra et al., 2020) found impact strength peaks at 80-85% infill, not 100%. At 100%, the part is too homogenous and cracks propagate easily. Use 80-85% gyroid for maximum impact resistance. Reserve 100% for tiny cosmetic parts only.
What about wall line count vs shell thickness?
Same concept, different slicer terminology. Cura uses "wall line count", PrusaSlicer uses "perimeters". 4 walls ≈ 1.6mm shell with 0.4mm nozzle.
Does infill pattern really matter?
Yes. Gyroid and honeycomb are isotropic (equal strength all directions). Grid and lines are weaker perpendicular to the lines. For automotive parts under varied loads, gyroid wins.
Should I increase walls or infill for a part that broke?
Check where and how it broke. Cracked at the surface after many flex cycles = too rigid, try fewer walls with more infill. Crushed or collapsed internally = add infill. For clips, 3 walls with 70-80% infill is usually the answer.
Troubleshooting
Part is too heavy
Use gyroid pattern which prints faster than grid. Consider 50-60% instead of 70%+ for non-critical parts.
Clip snaps after a few uses
Increase wall count to 4-5. Check layer orientation - print so layers align with stress direction.
Part flexes too much
Add walls for stiffness. If it's a large flat part, add ribs in your model design or increase infill.
Top surface has gaps or pillowing
Infill is too low to support top layers. Increase to 40%+ or add more top layers in slicer.
Ready to Print Stronger Parts?
Apply these settings to your next automotive print project.