Printing Guide

Wall Thickness & Perimeters

Walls are the primary load-bearing structure of FDM prints - more important than infill for most strength applications. Here's how to use them correctly.

Walls vs Infill

In FDM printing, the outer perimeters (walls/shells) carry the vast majority of the structural load. Infill mainly supports top surfaces and adds compression resistance. This is why adding a wall perimeter almost always gives more strength per print-minute than raising infill by 10%.

With a 0.4mm nozzle at standard line width:

  • 1 wall = 0.4mm
  • 2 walls = 0.8mm
  • 3 walls = 1.2mm (most common functional default)
  • 4 walls = 1.6mm (recommended for mechanical parts)
  • 5 walls = 2.0mm
Line Width
Typically 100-120% of nozzle diameter. [1] 0.4mm nozzle = 0.4-0.48mm line width. Most slicers default to 0.45mm.
Wall Count vs Thickness
Set by count (number of perimeters) or mm. Match to your nozzle: wall thickness should ideally be a multiple of your line width.
Outer vs Inner Walls
Outer walls print slower for quality. Inner walls fill in strength. A single outer + multiple inner walls is common.
Vase Mode
1 continuous wall spiraled outward. Fastest possible single-wall print. Zero structural value - purely visual.

Wall Count Effects

Property 2 Walls 3 Walls 4-5 Walls 6+ Walls
Tensile strength (Z axis) Weak Adequate Good Very good
Tensile strength (XY plane) Adequate Good Very good Excellent
Surface quality Adequate Good Excellent Excellent
Watertightness No Rarely Often Yes
Impact resistance Low Medium Good Very good
Part weight Light Medium Heavy Very heavy
Print time Fast Medium Slow Very slow
3 walls is the minimum for any functional part. 4 walls is the better default for anything load-bearing. [2]
For snap-fit features, living hinges, or thin walls: 2-3 walls in PETG or PLA+ often gives the right balance of flex and strength. PLA is too brittle for repeated snap-fit use.

Printing Watertight Parts

Watertightness in FDM is primarily a function of wall count, material choice, and layer adhesion - not infill. A well-tuned 4-wall PETG print at 0.2mm layer height is typically watertight for static containers.

PLA is less reliably watertight even with high wall counts due to micro-gaps at layer boundaries - PETG is the recommended material for watertight prints.

Recipe for watertight containers: PETG, 4+ walls, 4 top/bottom layers, 40%+ infill, 0.2mm layer height. Tune flow rate to avoid under-extrusion.
PVA glue coating applied to the inside of a printed container seals micro-gaps effectively and is food-safe. Epoxy resin coating (XTC-3D) is stronger and suitable for outdoor use.
ABS and ASA can be acetone-smoothed for a near-hermetic seal - the most reliable post-processing method for watertight parts.
Textured top and bottom surfaces increase leakage risk - use smooth PEI and increase top/bottom layer count if watertightness is critical.

Layer Height and Wall Quality

Layer height affects wall quality through two mechanisms: bond strength between layers, and how well the slicer can place lines to build up the wall profile. Thinner layers (0.1-0.15mm) produce stronger Z-axis bonds and finer detail; thicker layers (0.3mm) print faster but have weaker interlayer adhesion.

0.1-0.15mm (Fine)
Strongest Z bonds, best detail. Slow. For functional small parts where Z strength matters.
0.2mm (Standard)
Universal default. Best balance of speed, strength, and surface quality. Use this unless you have a specific reason not to.
0.3mm (Draft)
Faster, noticeably layered surface, weaker Z bonds. For rapid prototypes only.
Top/Bottom Layers
Use 4-5 layers minimum regardless of layer height. At 0.2mm: 5 layers = 1mm solid bottom/top.

Settings by Use Case

Use Case Walls Layer Height Notes
Visual / decorative 2-3 0.15-0.2mm Surface quality priority; low infill OK
Snap-fit / clips 3-4 0.2mm PETG or PLA+ recommended; PLA too brittle
Functional brackets 4 0.2mm 25-40% gyroid infill to match
Mechanical load-bearing 4-5 0.2mm Consider material: PETG minimum
Watertight container 4+ 0.2mm PETG; 4 top/bottom layers; 40% infill
Living hinge 2 thin walls 0.15-0.2mm TPU or flexible PLA; 0% infill at hinge
Maximum strength 5-6 0.15-0.2mm More walls > more infill for tensile loads

Common Mistakes

Using 2 walls for functional parts. Two walls is often fine for visual prints but provides minimal structural integrity for parts under any real load.
Raising infill instead of walls. A 4-wall 20% infill print is stronger than a 2-wall 60% infill print for tensile loads. [2] Walls are load-bearing; infill supports tops and compression.
Designing thin walls that aren't multiples of line width. A 0.6mm wall with a 0.45mm line width produces mixed results - the slicer may fill it with partial lines or infill. Design walls to be exact multiples of your nozzle's line width.
Expecting watertightness from PLA. Even 6-wall PLA prints often seep. PETG is the right material choice for watertight applications.
Vase mode for functional parts. Vase mode (1 continuous wall) is beautiful but structurally near-zero. It's a visual technique only.
Browse Filament on SpoolHound Infill Patterns Guide →

References

  1. Prusa Knowledge Base — "Layers and Perimeters." help.prusa3d.com/article/layers-and-perimeters_1748
  2. CNC Kitchen — "Gradient Infill for 3D Prints" — how perimeter proximity affects strength more than uniform infill density. cnckitchen.com/blog/gradient-infill-for-3d-prints