That is under-extrusion: the printer is laying down less plastic than the slicer planned. Common causes are a partial clog, wet or tangled filament, a slipping extruder, a temperature too low for the material, or flow and diameter settings that do not match the filament.
Gaps between walls, weak top surfaces and thin lines all point to too little plastic reaching the part.
Check the filament path
Spool turns freely and is not tangled. Filament is dry and the right diameter. Bowden tube or feed path is not kinked or worn.
Check the extruder
Tension on the filament, clean gears without plastic dust, and no clicking or grinding. Worn or dirty gears slip.
Check the hotend
Partial clogs from debris or heat creep. Temperature at the low end of the filament maker’s range can limit flow, especially at high speeds. Nozzle wear from abrasive filaments.
Check the slicer
Filament diameter setting matches the spool. Flow or extrusion multiplier has not been changed by accident. Speed is not higher than the hotend can melt for that material.
Calibrate last
Once mechanical causes are ruled out, calibration tests in the slicer confirm flow and extrusion settings for the filament in use.
Questions makers ask before buying
How can I tell whether the extruder is slipping?
Clicking sounds, ground-down filament with bite marks and uneven lines are signs. Checking extruder tension and cleaning the gears are the usual first steps.
Should I just increase the flow rate?
Only after ruling out mechanical causes. Raising flow to hide a clog or slipping extruder masks the problem until it gets worse.
Last reviewed 15 September 2026