How to Fix a Rough PETG Surface
Healthy PETG has a signature look: glassy, slightly translucent, almost injection-moulded. When PETG walls come out grainy, pitted or fuzzy instead, the material is announcing — louder than any other filament — that it has been drinking. Moisture is cause number one, with speed and flow far behind.
PETG is a moisture meter with a nozzle
PETG absorbs water within days on an open shelf, and at 250 °C that water flashes to steam in the melt. Bubbles burst at the surface and leave pits; micro-foaming kills the gloss; ejected droplets land as fuzz. The result reads as “rough surface” but is really “wet spool”:
Dry PETG for 8 h at 65 °C and reprint the same file. Compare walls side by side. In most cases this single step restores the gloss outright — and if it does, the fix going forward is storage, not settings: sealed box, silica, always. Per-brand drying specs in the drying guide.
The confirmation signs, in rough order of appearance as a spool gets wetter: gloss fades to satin → occasional pits → audible crackle at the nozzle → stringing everywhere → visibly foamy extrusion. By the crackle stage no slicer setting matters.
If the spool is dry: speed and vibration
Slow the outer wall. Ripples that repeat after corners and edges are ringing — the machine vibrating, not the material failing. Drop the outer wall to 100–120 mm/s (inner walls and infill can stay fast) and re-run the printer’s vibration calibration if it has been moved. PETG’s gloss makes ringing more visible than on matte materials, so PETG is often just the messenger.
Calibrate flow for generic spools. Stock flow ratio is 0.95; a spool that needs 0.92 will plough its top surfaces and pile micro-blobs on walls. The slicer’s flow calibration pins it in fifteen minutes.
PETG-specific surface notes
- Nozzle crust rain. PETG builds a crust of cooked material on the nozzle over hours, which detaches as brown specks onto walls. Brush the hot nozzle (brass brush, gently) before big prints, and keep z-hop on so the tip doesn’t rub the part.
- Temperature vs. gloss: hotter PETG within its 230–270 °C range prints glossier; the cool end goes satin. That is aesthetics, not a defect — pick the finish you want.
- Overhang grain is normal: undersides of overhangs print rougher on PETG because its cooling window (30–60 %) is modest. The stock profile boosts fan to 90 % on overhangs; steeper than ~50° wants support, not more fan.
The one-print diagnosis
Print a 30 mm cube: all four walls equally grainy → moisture (or flow, if drying changed nothing). Ripples after corners only → speed/vibration. One wall rougher than the others → airflow hitting that side (drafts, or the auxiliary fan on enclosed machines — PETG’s profile wants it at 0 %). The general surface-quality decision tree, including worn nozzles and partial clogs, is in the rough surface guide; PETG’s full sheet in the PETG settings guide.
Frequently asked questions
Why does my PETG print have a rough, grainy surface?
Moisture is cause number one. PETG absorbs water within days on an open shelf, and at 250 °C that water flashes to steam in the melt: bursting bubbles leave pits, micro-foaming kills the gloss, and ejected droplets land as fuzz. Speed and flow come far behind. The escalation as a spool gets wetter: gloss fades to satin, then pits, then audible crackle at the nozzle, then stringing everywhere.
How long should I dry PETG filament?
Dry PETG for 8 hours at 65 °C, then reprint the same file and compare walls side by side. In most cases this single step restores the gloss outright — and if it does, the fix going forward is storage, not settings: sealed box with silica, always. If drying changes nothing, calibrate flow: stock flow ratio is 0.95, and a spool needing 0.92 will pile micro-blobs on walls.
How do I tell if PETG roughness is moisture or vibration?
Print a 30 mm cube. All four walls equally grainy points to moisture (or flow, if drying changed nothing); ripples that appear only after corners are ringing — the machine vibrating, not the material; one wall rougher than the rest means airflow hitting that side, from drafts or the auxiliary fan, which PETG’s profile wants at 0 %. For ringing, drop the outer wall to 100–120 mm/s.
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- Filament Drying Recommendations — Bambu Lab Wiki
- Common print quality problems and solutions — Bambu Lab Wiki