PLA under-extrusion is what you see when the printer lays down less PLA than the layer needs, so the walls go thin, the top fails to close, and the infill looks sparse. The cause is usually a partial clog, a flow set too low, or a nozzle that runs too cold. Bambu’s under-extrusion guide and PLA page point there.
The fix runs from a quick slicer change to a hardware clean. Work the list in order and reprint the same one-wall test after each step.
PLA melts clean at a low temperature, near 200 to 210 C, so a temp set too low starves it.
The causes, ranked
| Likely cause | Fix | Severity |
|---|---|---|
| Partial clog | Run a cold pull to clear the blockage, then push fresh PLA through. | hi |
| Flow too low | Raise the flow a few percent and reprint. | hi |
| Nozzle too cold | Raise the nozzle toward 200 to 210 C so the PLA melts fully. | hi |
| Extruder gear slip | Tension the idler and clean the gear teeth so they grip the PLA. | md |
| Wet PLA | Dry the spool at 40 to 50 C, then reprint. | lo |
First fixes to try
Print a one-wall PLA cube and pinch a wall, then work top to bottom and reprint after each step.
Raise the nozzle temp
Set the nozzle toward 200 to 210 C so the PLA melts clean.
Raise the flow
Bump the extrusion multiplier up a few percent and reprint.
Run a cold pull
If the flow change does nothing, clear a partial clog with a cold pull and retest.
Dry the PLA
If the print is rough, dry the spool at 40 to 50 C and reprint.
When quick fixes are not enough
When flow and temp do not fill the walls, the extruder and the path are next.
Tension and clean the gear
Set the idler to a light, even grip and brush the extruder gear clean.
Check the Bowden path
On a Bowden machine, look for a loose coupling or a tube gap that chokes flow.
Recalibrate e-steps
Mark 100 mm of PLA, command a 100 mm feed, and trim the e-steps to match.
How PLA differs
PLA under-extrudes the least of the common filaments when it is dry, because it melts clean at a low temperature near 200 to 210 C. PETG and nylon under-extrude more when wet, since they pull in moisture fast and the water thickens the melt. PLA soaks up less water, so a dry spool prints full with little fuss.
Mistakes that keep PLA thin
A few choices fix the look and leave the cause.
Avoiddo not
- Raising the flow so far the top layers bulge.
- Running PLA too cool, which starves the walls.
- Leaving a slipping extruder gear and blaming the flow.
- Changing flow, temp, and tension in one pass.
Key takeaways
- PLA under-extrudes from a clog, low flow, or a cold nozzle.
- Raise the nozzle toward 200 to 210 C and the flow a few percent.
- Clear any clog and tension the extruder gear.
- PLA under-extrudes less than PETG when it is dry.
For the general version, the under-extrusion guide covers any filament, and the PLA hub covers the material in depth.
Related guides
Related
More in this area
Cross-reference
Sources & methodology
3 citations · reviewed 2026-07-10- 01Bambu Lab Wiki: Under-extrusion (flow volume, resistance, pressure advance)accessed 2026-07-09Tier 1
- 02Bambu Lab PLA Usage Guide (wiki): PLA nozzle and flowaccessed 2026-06-29Tier 1
- 03All3DP: Under-extrusion causes and fixesaccessed 2026-07-09Tier 2