Under-Extrusion: Why Your Printer Isn't Pushing Enough Plastic

Under-extrusion is when your printer lays down less plastic than the model needs. You'll see it as gaps between lines, thin or missing top layers, weak walls that pull apart, and a generally starved, patchy surface. It's one of the most common print-quality problems — and because several different things cause it, the fix is about working through them in order. Here's how.

How to Recognise It

Under-extrusion shows up as: visible gaps between adjacent lines, layers that don't bond and split apart, holes or thin spots in the top surface, stringy or skipped infill, and parts that feel brittle. If walls look starved and you can see through to the infill, that's the signature.

Fix It in This Order

1. Check for a Partial Clog

The most common cause. A partially blocked nozzle restricts flow — the printer tries to push plastic but can't get enough through. Signs: clicking from the extruder, inconsistent flow, or it gradually worsening over a print. Do a few cold pulls (atomic pulls) to clear debris, or run a cleaning filament. If a nozzle is worn or stubbornly blocked, swap it — nozzles are consumables. Keeping filament dry and clean prevents most clogs.

2. Dry Your Filament

Wet filament foams and spits at the nozzle, disrupting steady flow and mimicking under-extrusion. If the spool's been open a while, dry it (45–55 °C for several hours) and store it sealed with desiccant. Our Spain-made filament ships sealed and dry, with tight diameter tolerance — thin spots in cheap filament are themselves a cause of under-extrusion.

3. Raise the Temperature

If the nozzle isn't hot enough, plastic can't melt fast enough to keep up with the flow rate — especially at speed. Raise the temperature in 5 °C steps. A temperature tower finds the point where flow becomes consistent.

4. Calibrate Flow Rate

If flow is simply set too low, every line comes out thin. Run a flow-rate (extrusion-multiplier) calibration and set the correct value in your profile. Our flow test guide walks through it, and the Orca Slicer calibration guide shows the two-pass method.

5. Slow Down (or Lower Max Volumetric Speed)

Every hotend has a limit to how fast it can melt plastic. Push past it and the printer physically can't extrude enough — under-extrusion at high speed even though slow prints are fine. Lower print speed, or calibrate Max Volumetric Speed to find your hotend's real ceiling.

6. Check the Extruder Itself

A worn extruder gear, weak idler tension, or a slipping drive can fail to grip the filament. Look for chewed filament or gear marks. Check tension and that the gear teeth are clean. See our extruder calibration guide to confirm it's pushing the right amount.

Quick Diagnostic

The Filament Factor

Cheap filament with loose diameter tolerance causes intermittent under-extrusion that no amount of tuning fully fixes — thin spots simply deliver less plastic. Our PLA, PETG, TPU, ABS, and ASA are made in Spain to ±0.05 mm (±0.08 mm on TPU) and sealed dry, removing two of the biggest causes before you start. Once you've ruled out filament, the settings fixes above will hold. Still under-extruding? Tell us your printer and material and we'll help narrow it down.