For an roughly 8-inch (about 200 mm) sided part printed in PETG, where some flexing is acceptable and your main goals are minimizing print time and material use, a reasonable wall thickness is in the range of 1.2–1.6 mm.
This strikes a very good balance for most non-load-bearing or lightly loaded enclosures, covers, cases, brackets, or decorative/functional parts of that size.
Why this range?
- 1.2 mm (often 3 perimeters / wall loops with a standard 0.4 mm nozzle) — This is the most common “minimum for decent strength” recommendation across many PETG guides and community sources. It gives good structural integrity for general use, resists most print failures or weak spots, and keeps material/print time quite low. PETG’s excellent layer adhesion and impact resistance make 1.2 mm behave noticeably better than the same thickness in PLA.
- 1.6 mm (typically 4 perimeters) — A sweet spot if you want noticeably more stiffness and durability while still being fairly efficient. It adds only ~30% more perimeter extrusion time compared to 1.2 mm but feels much more solid and reduces the “floppy” feeling on larger flat panels.
- Below 1.2 mm — Possible (e.g., 0.8–1.0 mm), but riskier on an 8" part. You may get visible flexing/buckling on flat walls, especially under any pressure or if the part has large flat areas. Voids can appear if the thickness isn’t a clean multiple of your extrusion width.
- 2.0 mm+ (5+ perimeters) — Usually unnecessary if flex is okay and you’re optimizing for speed/material. This is more for mechanically loaded parts (brackets under constant stress, tool holders, etc.).
Practical slicer recommendations (assuming standard 0.4 mm nozzle)
- Wall loops / perimeters → 3–4
- Wall thickness → 1.2–1.6 mm (most slicers let you set this directly; the slicer will snap to clean perimeter counts)
- Infill → 10–20% (gyroid or cubic are great for balancing strength vs speed when walls are fairly thin)
- Top/bottom layers → 0.8–1.2 mm total thickness (4–6 layers at 0.2 mm layer height) is usually plenty
Quick comparison for an ~8" sided box-like part
- 1.2 mm walls + 15% infill → fastest/lightest reasonable option, will flex noticeably when you push on large flat faces
- 1.6 mm walls + 15% infill → ~20–35% more perimeter time, but much less floppy, better feel overall
- 2.0 mm walls → significantly more material/time (~60%+ more perimeter plastic than 1.2 mm), usually overkill if flex is allowed
Start with 1.2–1.4 mm (3–3.5 perimeters), print a quick test section or the full part, and see how much flex you actually get. PETG is forgiving—if it’s too floppy, bump up one perimeter (adds very little time compared to reprinting at 2+ mm walls).
If your part has very large flat panels (>150–200 mm) without ribs/bracing, consider adding some internal ribs or gussets instead of just thickening every wall—that usually saves more time/material than blanket-thick walls.