Blobs and zits are the small lumps and surface pimples that scatter across a print, most often where a perimeter starts or stops. They form when the nozzle oozes a little extra filament during a travel move or at the seam. Per Bambu’s stringing-and-oozing guide, the cause is almost always a mismatch between the pressure in the nozzle and the move the slicer asked for.
The fix lives in a short list of slicer settings and one hardware habit. Work through the causes in order and reprint the same test after each change.
The material changes the count. PETG oozes more than PLA and blobs worse when it is wet, while PLA stays cleaner at the seam.
Likely causes, ranked
| Likely cause | Fix | Severity |
|---|---|---|
| Retraction too low or off | Raise retraction distance a step at a time. Direct-drive lands near 0 to 2 mm, Bowden near 1 to 6 mm. | hi |
| Pressure advance or coasting off | Turn on coasting in Cura, or wipe while retracting in PrusaSlicer, Bambu Studio, or OrcaSlicer. | hi |
| Nozzle too hot | Drop the nozzle 5 to 10 C and reprint. Most filaments ooze less near the low end of their range. | md |
| Outer wall speed too high | Slow the outer wall to 25 to 30 mm/s so the seam lays down clean. | md |
| Wet filament | Dry the spool, then reprint. PETG blobs more once it takes on water. | lo |
Quick fixes to try first
Print a simple test cube and watch the seam, then work top to bottom and reprint after each step.
Raise retraction
Add a little retraction distance, reprint, and look for fewer blobs at the seam.
Turn on pressure relief
Enable coasting in Cura, or wipe while retracting in PrusaSlicer, Bambu Studio, or OrcaSlicer.
Drop the nozzle temp
Lower the nozzle 5 to 10 C and reprint. Stop at the lowest temp that still lays strong layers.
Slow the outer wall
Set the outer wall to 25 to 30 mm/s and reprint for a cleaner seam.
Dry the filament
If blobs come with strings or a rough surface, dry the spool and reprint.
Deeper tuning to try next
When retraction and temperature do not clear the blobs, the pressure control and the hardware are the next place to look.
Tune pressure advance
On Klipper or a printer that supports it, adjust pressure advance so the extruder eases filament pressure at the seam.
Check the extruder hardware
A partly clogged nozzle or a loose Bowden coupling causes uneven flow that reads as blobs. Clean and tighten before you blame the slicer.
Move the seam
Set the Z-seam to a corner or the back, where a small zit hides instead of sitting on the show face.
How the material changes things
PETG oozes more than PLA at print temperature, so it blobs and strings more, and a wet PETG spool makes it worse. PLA stays clean at the seam when it is dry and the retraction is set. TPU is flexible and needs slow speeds and short retractions to keep blobs down.
Mistakes that bring it back
A few common habits hide the real cause or bring the blobs back.
Avoiddo not
- Turning retraction up far past the useful range. It starves the extruder and causes under-extrusion.
- Leaving coasting or wipe at an extreme value. Too much opens gaps at the seam.
- Skipping the dry step for PETG. Wet PETG blobs no matter the slicer settings.
- Changing retraction, temperature, and speed in one pass, so the real cause stays hidden.
Key takeaways
- Blobs and zits come from extra filament at the seam, driven by retraction and nozzle pressure.
- Work the list: retraction, pressure relief, then temperature.
- Dry PETG first. Wet filament blobs and strings more.
- Change one setting and reprint the same test.
For related problems, the stringing guide covers the fine hairs between moves, 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- 01Bambu Lab Wiki: Stringing and oozing (retraction, temperature, damp filament)accessed 2026-07-09Tier 1
- 02All3DP: Zits and blobs (surface fixes)accessed 2026-07-09Tier 2