Over-extrusion is what happens when the printer pushes more filament than the layer needs. The top layers bulge, the walls feel thick or rough, and fine details fill in with extra plastic. Per Bambu’s print-quality catalogue, the cause is almost always the extrusion multiplier or flow set too high, a wrong filament diameter, or a worn nozzle.
The fix is mostly a slicer setting and a quick hardware check. Work the causes in order and reprint the same calibration test after each change.
The material does not drive over-extrusion. Any filament over-extrudes the same way when the flow is too high, though a wet spool can add a little extra volume as steam pushes plastic out.
Causes, in order
| Likely cause | Fix | Severity |
|---|---|---|
| Extrusion multiplier or flow too high | Lower the flow or extrusion multiplier a few percent and reprint. | hi |
| Filament diameter set wrong | Set the filament diameter to 1.75 mm in the slicer. | hi |
| Nozzle temp too high | Lower the nozzle about 5 C so the filament runs less runny. | md |
| Worn nozzle wider than spec | Swap in a new nozzle of the right size. | md |
| E-steps set too high | Recalibrate the extruder steps against a measured 100 mm. | lo |
Quick fixes to try first
Print a simple one-wall cube or a flat top test, then work top to bottom and reprint after each step.
Lower the flow
Drop the extrusion multiplier or flow by a few percent and reprint.
Check the filament diameter
Confirm the slicer is set to 1.75 mm, the standard for almost all desktop filament.
Lower the nozzle temp
Cut the nozzle about 5 C and reprint if the walls still look fat.
Dry the filament
If the surface is rough and pops, dry the spool, since wet filament can add volume.
Deeper tuning to try next
When the flow and the temps look right, the hardware and the calibration are the next place to look.
Inspect the nozzle
A nozzle worn wide by use lays too much plastic. Swap in a new one of the right size.
Recalibrate e-steps
Mark 100 mm of filament, command a 100 mm feed, and trim the e-steps until it matches.
Measure the filament
Some spools run thick. Measure with calipers and, if needed, set the real diameter in the slicer.
How the material changes things
Over-extrusion is the same across PLA, PETG, and the rest when the flow is too high. A wet spool can make it worse, since boiling moisture pushes extra plastic out at the nozzle. PETG shows over-extrusion as rough, droopy top layers more clearly than PLA, so it is a good material to tune flow on.
Mistakes that bring it back
A few common choices swing the print the other way.
Avoiddo not
- Dropping the flow so far the top goes thin and the walls gap.
- Setting the diameter by guess instead of a real measurement.
- Ignoring a worn nozzle and blaming the flow instead.
- Changing flow, temperature, and diameter in one pass, so the real cause stays hidden.
Key takeaways
- Over-extrusion lays too much filament, from flow, diameter, or a worn nozzle.
- Lower the flow a few percent and confirm 1.75 mm first.
- Swap a worn nozzle and recalibrate e-steps if it returns.
- Change one setting and reprint the same test.
For the 3D-print-specific version, the over-extrusion on a 3D print page covers the same fault from a symptom-first angle. For the opposite problem, the under-extrusion guide covers thin walls and gaps, and the filament storage guide covers keeping spools dry.
Related guides
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Sources & methodology
2 citations · reviewed 2026-07-10- 01Bambu Lab Wiki: Common print quality problems (over/under-extrusion)accessed 2026-07-09Tier 1
- 02All3DP: Over-extrusion causes and fixesaccessed 2026-07-09Tier 2