Over-Extrusion, Blobs and Zits: How to Fix Too Much Plastic

If under-extrusion is too little plastic, over-extrusion is too much — and it brings its own set of problems: rough, bulging surfaces, parts that come out larger than designed, blobs and 'zits' on the walls, and elephant's foot at the base. The good news is that over-extrusion is one of the most directly fixable defects, because it almost always comes down to calibration. Here's how to dial it out.

What Over-Extrusion Looks Like

Watch for: walls that look swollen or rough rather than crisp, top surfaces that are bumpy or 'over-filled', dimensions coming out oversized, blobs and pimples (zits) on the surface, stringing combined with excess material, and elephant's foot — the bottom layers bulging out wider than the rest.

Fix It in This Order

1. Calibrate Flow Rate (Extrusion Multiplier)

The number-one cause. If flow is set too high, every line puts down too much plastic. Run a flow-rate calibration and reduce the multiplier until walls come out crisp and dimensions are accurate. This single step fixes most over-extrusion. Our flow test guide and the two-pass method in the Orca Slicer calibration guide walk through it.

2. Check Filament Diameter Setting

Your slicer assumes a filament diameter (usually 1.75 mm). If that figure is wrong — or your filament is inconsistent and actually runs thicker — the printer pushes too much. Confirm your slicer's diameter matches your filament. Consistent filament matters here: our Spain-made filament holds ±0.05 mm tolerance, so the 1.75 mm setting is accurate spool to spool.

3. Lower the Temperature

Printing too hot makes plastic runnier, so it oozes and spreads more than intended — contributing to blobs and rough surfaces. Drop the temperature in 5 °C steps; a temperature tower shows the cleanest setting.

4. Tune Pressure Advance / Linear Advance

Blobs and zits often appear where the nozzle starts, stops, or changes direction — pressure builds in the nozzle and releases as a blob. Calibrating pressure advance (linear advance) evens out that pressure for clean corners and seams. The Orca Slicer calibration guide covers this step.

5. Enable Coasting and Wipe

In your slicer, 'coasting' stops extrusion just before the end of a line to release pressure, and 'wipe' moves the nozzle over the printed line to clean off excess. Both reduce blobs and zits at the seam.

6. Fix Elephant's Foot Specifically

If only the base bulges, it's a mix of over-extrusion and a bed that's too hot or a nozzle too close on the first layer. Lower the first-layer flow or bed temperature slightly, and use your slicer's 'elephant's foot compensation'. Our first-layer guide covers Z-offset, which interacts with this.

Quick Diagnostic

Over vs Under: The Same Calibration Solves Both

Over- and under-extrusion are two ends of the same dial. If you've read our under-extrusion guide, you'll recognise the tools — temperature tower, flow test, pressure advance — because dialling them in correctly is what keeps you in the sweet spot between the two. Get the calibration right once on consistent filament and both problems disappear.

Start With Filament You Can Trust

Accurate flow calibration depends on filament that's actually the diameter it claims. Our PLA, PETG, TPU, ABS, and ASA are made in Spain to tight tolerances, so once you calibrate flow, it stays correct. Fighting blobs or oversized parts you can't tune out? Get in touch and we'll help.