Main site nadinmacht.deDeutsch

Fixing under-extrusion: gaps and thin walls

Troubleshooting6 min readUpdated: 10/2026

are explained briefly when you hover over or tap them.

With under-extrusion, less plastic comes out of the nozzle than the printer actually wants to lay down. The result is gaps between the lines, thin or holey walls and surfaces through which you can see the infill. In the worst case the print stops altogether because nothing comes out at all.

Too little material thin strand Gaps between the lines Goal: right amount Lines meet with no gaps
Schematic, cross-section through one layer. On the left too little plastic comes out of the nozzle, so the lines are thin and leave gaps. On the right they are full and touch each other.

How can you recognise under-extrusion?

  • Gaps between the lines, especially on the top surface
  • Thin, fragile walls that are easy to dent
  • Missing lines in individual layers
  • Clicking or rattling noise at the extruder: the gear slips because the filament does not keep up
  • The top looks like a mesh instead of a closed surface

The causes, sorted by frequency

1. Too fast for the hotend

Every hotend can only melt a certain amount of plastic per second. If printing is faster, the material cannot keep up. This happens especially with large nozzles, tall layers or very fast profiles.

Solution: Reduce the speed or set a maximum volumetric flow for the filament in the slicer. In OrcaSlicer the right value can be determined with a built-in test. A somewhat higher temperature also helps, see Setting the print temperature.

2. Partially clogged nozzle

Small residues in the nozzle narrow the opening. The printer keeps printing, but with less material.

Solution: Clean or replace the nozzle. How this works is covered under Clogged nozzle.

3. Temperature too low

If the plastic is not fluid enough, it flows too slowly through the nozzle.

Solution: Raise the temperature in steps of 5 degrees and observe the manufacturer’s figure on the spool.

4. Problems with the filament

  • Tangled or jammed spool: The filament cannot unwind freely. Check the spool and make it run smoothly.
  • Damp filament: Steam bubbles disturb the material flow. More on this in Drying and storing filament.
  • Fluctuating diameter: With very cheap filament the diameter can fluctuate strongly. Test with a different spool.

5. Extruder not gripping properly

If the contact pressure of the gears is too low or they are dirty with plastic shavings, the filament slips.

Solution: Clean the gears with a small brush and check the contact pressure according to the manufacturer’s instructions.

6. Wrong flow value in the slicer

The flow factor (flow rate) determines how much material is fed. If it is set too low, material is missing.

Solution: Carry out a flow calibration. Many current printers and slicers offer an automatic or built-in test for this.

Quick checklist

  1. Does a different filament print cleanly? Then the material is the cause.
  2. Does printing more slowly help? Then the hotend was at its limit.
  3. Does the extruder click? Then check the nozzle and temperature.
  4. When extruding manually, does an even, straight strand come out of the nozzle? If not, the nozzle is probably partially clogged.

The opposite, too much material, shows up as bulges, rough surfaces and dimensions that are too large. Flow calibration helps in that case too.