UNDER-EXTRUSION REPORT
Under-extrusion is the symptom. The useful question is where the restriction or mismatch starts: nozzle, temperature/profile, feed path or filament condition.
TRIAGE ORDER
01 · Clog
Start here if purge flow is weak, curls sharply, or the extruder clicks under load.
02 · Profile
Check nozzle type, temperature, speed and volumetric-flow mismatch.
03 · Feed path
Inspect spool movement, PTFE routing and drive gears for drag or grinding.
04 · Moisture
Move it up the list only when popping, bubbles or exposure history support it.
What under-extrusion looks like
Gaps
Visible spaces in walls or top surfaces.
Thin lines
Extrusion lines are incomplete or narrower than expected.
Weak sections
Missing material can make parts fragile even when bonding is otherwise normal.
CAUSE CHECK
Partial clog first
Prusa describes a partial clog as a state where some filament still comes out, but not enough for normal printing. Strong clues include inconsistent purge flow, a strand curling back toward the nozzle, clicking or grinding and the same issue across different files.
How to separate clog from moisture
| Clue | More consistent with clog | More consistent with moisture |
|---|---|---|
| Sharp curling purge strand | Yes | Weak clue |
| Extruder clicking | Strong clue | Possible but not diagnostic |
| Popping / crackling | Not typical alone | Strong supporting clue |
| Bubbles / rough extrusion | Less characteristic | Supports moisture |
| Problem persists with known-good spool | Supports machine-side restriction | Weakens moisture hypothesis |
Best test sequence
- Purge filament and watch the strand closely.
- Check spool movement and the entire feed path.
- Confirm the correct nozzle/profile combination and manufacturer printing range.
- If clog clues are strong, investigate the nozzle/hotend before tuning flow.
- If moisture clues are strong, use exact-product drying guidance and repeat the same print without unrelated changes.
Missing material is not a diagnosis.
Do not compensate for a restriction by blindly increasing flow. Find the bottleneck first.
Sources
Prusa — Under-extrusion · Prusa — Clogged nozzle · Prusa — Drying filament. Checked September 13, 2026.