How to Fix PLA Over-Extrusion

Over-extruded PLA looks 'melted': ridges the nozzle ploughs through on top surfaces, blobs at corners and seams, holes that measure small and outer dimensions that measure fat. The extruder is simply pushing a few percent more plastic than the line needs — and with PLA the calibration to fix it takes fifteen minutes.

Where the extra plastic comes from

Slicers compute exactly how much filament each line needs, scaled by the profile’s flow ratio. Bambu’s PLA profiles ship at 0.98, tuned against Bambu’s own filament; most vendor baselines for generic PLA agree at 0.98, with outliers like RatRig’s at 0.92. A generic spool that runs thick (larger real diameter) or simply flows differently can effectively over-extrude by 2–5 % against these defaults — small enough to miss, big enough to ruin top surfaces and dimensional accuracy.

Fixes in order

Impostors: things that look like over-extrusion

• Elephant foot — a flared first few millimetres with clean walls above is a first-layer squish/heat effect, not global over-extrusion; see the elephant foot guide.
• A too-hot bed — PLA softens around 45 °C; a bed above 65 °C keeps the lower centimetre rubbery and bulgy while extrusion is actually correct. Stock textured-PEI bed is 55 °C.
• Seam blobs alone — if walls and tops are clean but seams carry a pimple, that is pressure/seam tuning, not flow. See the seam guide.

Verify with a single-wall test

Slice a calibration cube in vase/single-wall mode with a 0.42 mm line width (the common default on 0.4 mm nozzles) and measure the printed wall with calipers. Within a couple of hundredths of the target: flow is fine, look at the impostors above. Fat by 5 % or more: calibrate. This ten-minute check saves whole evenings of chasing symptoms one surface at a time. The cross-material picture — including how over-extrusion interacts with line width and why dimensional errors deserve their own compensation settings — is in the main over-extrusion guide; PLA’s value sheet in the PLA settings guide.