A rough top layer is a scarred, ridged, or gap-filled surface on the top of a print. Sometimes the infill pattern shows through, and sometimes the top skin never fully closes. Per Prusa’s infill guide, the cause is usually too little filament on top, infill too sparse to support it, or a nozzle that runs too close to the layer.
The top layer is the last thing you see, so a rough one stands out even when the rest of the print is fine. Work the causes in order and reprint the same test after each fix.
Your material changes the look. PETG shows roughness and ridges on top more clearly than PLA, and any wet filament makes the surface worse.
What drives it
| Likely cause | Fix | Severity |
|---|---|---|
| Under-extrusion on top | Raise the flow a few percent, and add a top solid layer or two. | hi |
| Infill too sparse | Raise the infill density or add more top layers so the skin has support. | md |
| Nozzle too close, Z-offset too low | Raise the Z-offset a touch so the nozzle does not gouge the top. | md |
| Nozzle temp too low | Raise the nozzle about 5 C so the top lays down smooth. | md |
| Wet filament | Dry the spool, then reprint. Wet filament lays a rough bead. | lo |
Quick fixes to start with
Print a small flat-topped test cube and run a finger over the top, then work top to bottom and reprint after each step.
Add top layers
Increase the number of top solid layers so the skin closes fully over the infill.
Raise the flow
Bump the extrusion multiplier up a few percent so the top fills in.
Raise the infill density
Add more infill so the top layers have something to rest on.
Raise the nozzle temp
Add about 5 C to the nozzle so the top bead lays down smooth.
When the basics are not enough
When flow and infill do not smooth the top, the ironing and the Z-offset are the next place to look.
Turn on ironing
Enable ironing on the top layer so the nozzle runs a hot pass over it to flatten the surface.
Raise the Z-offset
Lift the Z-offset a touch so the nozzle does not drag through the previous top layer.
Slow the top layer
Drop the outer and top layer speed for a cleaner skin.
How your material changes things
PLA lays the smoothest top layer when it is dry and the temp is set. PETG shows ridges and roughness on top more clearly, since it runs hotter and oozes, so it likes a slightly lower temp and a slower top layer. ABS and ASA can roughen if the chamber cools mid-print. A wet spool roughens every material, so dry first.
What not to do
A few common choices trade the roughness for a new problem.
Avoiddo not
- Raising the flow so far the top over-extrudes and bulges.
- Lowering the Z-offset to press the top, which gouges it instead.
- Leaving infill sparse and stacking more top layers to hide it.
- Changing flow, infill, and temp in one pass, so the real cause stays hidden.
Key takeaways
- A rough top layer comes from under-extrusion, sparse infill, or a low nozzle.
- Add top layers, raise the flow, and raise the infill density first.
- Turn on ironing and raise the Z-offset for a smooth skin.
- PETG shows roughness more; dry every material first.
For the thin-wall cause, the under-extrusion guide covers too little filament, and the filament storage guide covers keeping spools dry.
Related guides
Related
More in this area
Cross-reference
Sources & methodology
2 citations · reviewed 2026-07-10- 01Prusa Knowledge Base: Problems with Infill (top surface and gaps)accessed 2026-07-09Tier 1
- 02All3DP: Top layer gaps and linesaccessed 2026-07-09Tier 2