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Under-extrusion: gaps, weak walls and skipped lines

Symptom: Thin or missing lines, gaps between walls, weak layers.

Most likely causes

  • Partial clog
  • Flow / e-steps not calibrated
  • Printing faster than the hotend can melt
  • Wet or low-quality filament

Test in this order

  1. Cold-pull or clean the nozzle to clear partial clogs.
  2. Calibrate flow and extruder e-steps.
  3. Check your max volumetric flow with the flow calculator and slow down if needed.
  4. Dry the filament and retry.
Stop changing multiple settings at once. Note the model, filament condition and room conditions, then change one variable and compare the same test print.

Relevant starting profiles

PETG settingsChoose your printer for a hardware-aware profile
ABS settingsChoose your printer for a hardware-aware profile
Nylon (PA) settingsChoose your printer for a hardware-aware profile

Reviewed 2026-08-18. Results vary by filament formulation, moisture, nozzle and slicer.