Walls and Perimeters

Walls (perimeters) are the continuous loops that make the outer shell of your print. For most functional parts, adding walls (shell thickness) improves real-world toughness, screw-holding, and impact resistance more reliably than raising infill—especially on small parts where walls can consume most of the cross-section. Use the slicer preview to confirm you’re actually getting the intended number of perimeter loops in thin regions and around holes, then tune line width/speeds so the outer wall prints cleanly and accurately.

TL;DR

For stronger prints, increase wall count (perimeter loops) before you crank up infill, and verify in preview that thin sections still get all the loops you expect. If the part is failing by layer splitting, fix bonding (temp/cooling) rather than just adding more walls.

Cross-section showing outer wall, inner walls, and where infill starts; also shows how small parts can become “all walls.”

What “Walls/Perimeters” Means in the Slicer

Walls (also called perimeters) are closed loops printed around the outside of each layer. Most slicers treat the outer wall as the “finish” pass (better surface and accuracy) and inner walls as structure that builds thickness. After the slicer places the requested shell thickness, it fills the remaining interior with infill (if any).

Why walls often beat infill for strength

Many real loads are carried near the surface. In bending, the outside fibers see the highest tension/compression, so a thicker shell takes more of the load. Impacts and abrasion also attack the skin first. More walls add more continuous filament lines around the part, which helps resist cracking at corners, improves puncture/abrasion resistance, and gives screws more solid plastic to bite into. High infill with a thin shell can still fail by splitting the shell, crushing the surface, or tearing out around holes.

Wall controls you’ll see (and what they really change)

Wall count: Number of perimeter loops per layer. More loops usually increases toughness and stiffness and can help support top surfaces.
Wall thickness: Shell thickness target in mm. Often equals (wall count × line width), but slicers may adapt widths to fit features.
Line width: How wide each extruded line is. Wider lines make each wall thicker and can improve bonding, but can blur details and crowd small holes.
Outer wall speed: Slower outer walls usually improve surface finish and dimensional accuracy; faster can cause ringing and visible gaps.
Wall order: Inner-then-outer often gives the outer wall a better foundation; outer-then-inner can help preserve sharp outside corners on some geometries.

Practical starting points (0.4 mm nozzle)

Cosmetic shells: 2 walls (about 0.8 mm) with moderate infill.
General functional parts: 3 walls (about 1.2 mm).
Tough parts, clips, brackets, screw bosses, thin vertical fins: 4–5 walls (about 1.6–2.0 mm), then lower infill if you need to control time/material.
If the cross-section is nearly all walls, changing infill won’t do much; focus on layer bonding (temperature, cooling, and not printing too cold/too fast).

How to confirm your walls are doing what you think (Preview checklist)

Turn on line-type coloring and inspect thin areas: do you still get the intended number of loops, or does it collapse to a single line?
Inspect around holes and slots: are perimeters crowding the hole and making it smaller, or merging into a blob?
Check top surfaces: sparse infill plus too few walls can leave weak support under top layers, causing pillowing/pinholes.
Zoom into corners: perimeters should look continuous and evenly spaced; odd gaps often indicate line width/wall-thickness fit issues.

Common problems and first fix

Cracks at corners or the outer shell splits under load

Likely cause: Too few walls and/or weak layer bonding

Fix: Add 1–2 walls and improve bonding: slightly raise nozzle temperature; reduce excessive cooling (especially PETG/ABS/ASA).

Holes and thin sections print undersized, or walls merge together

Likely cause: Line width too large and/or too many walls for the feature size

Fix: Set line width closer to nozzle diameter, reduce wall count for that model, and re-check any horizontal expansion/XY compensation that could be shrinking holes.

Top surface has gaps, pillowing, or pinholes

Likely cause: Not enough support under top layers (few walls + sparse infill)

Fix: Add 1 wall or increase infill slightly; also ensure you have enough top layers for your layer height.

Print time jumps a lot after increasing walls

Likely cause: Perimeters dominate toolpath on small parts and detailed geometry

Fix: Keep walls where the part needs toughness, but consider reducing outer-wall speed changes or using fewer walls on cosmetic/non-loaded sections; don’t trade away walls if the failure is shell-related.