How to Fix Under-Extrusion on a 3D Printer (2026)

What Under-Extrusion Looks Like

Under-extrusion is when your printer extrudes less filament than the slicer expects. The result:

• Visible gaps between perimeter lines on the wall
• Transparent or weak sections in the print
• Missing infill or sparse infill that should be solid
• Layers separate easily when you try to break the print
• Inconsistent surface texture — patches of good extrusion next to starved areas

If your print looks like it’s “starving” — not enough material — you’re under-extruding.

Step 1: Check Filament First

Before tweaking printer settings, rule out the obvious:

Wet Filament

Moisture in filament causes steam pockets during extrusion, which displaces plastic and creates voids that look like under-extrusion.

Diagnose: Listen during printing. Hissing or popping sounds = wet filament.

Fix: Dry the filament at 40-50°C for 4-6 hours in a filament dryer or food dehydrator.

See Best Filament Dryer for tested options.

Bad Filament Quality

Cheap filament with diameter variations (±0.1mm or worse) extrudes inconsistent amounts.

Diagnose: Measure the filament with calipers along 5-10 spots in a meter. If variance is over ±0.05mm, suspect the filament.

Fix: Switch to a tighter-tolerance brand. See Best PLA Filament .

Tangled Spool

Filament catching on the spool or itself causes intermittent extrusion stops.

Diagnose: Watch the spool during a print. If it tugs and jerks instead of unspooling smoothly, you have tangling.

Fix: Re-spool the filament manually, or switch to a brand with better spool winding (Hatchbox, Polymaker).

Step 2: Check Nozzle Temperature

Filament needs enough time at temperature to fully melt. If you’re printing too cold (or too fast for the temperature), filament arrives at the nozzle still partially solid.

Sweet spot ranges:

• PLA: 200-220°C (raise 5-10°C if printing fast)
• PETG: 230-250°C
• ABS: 230-250°C
• TPU: 220-240°C

The high-flow rule: For every 50mm/s of speed beyond 100mm/s, raise the nozzle temperature by 5°C. Bambu A1 at 500mm/s needs 220°C+ for PLA, not the standard 200°C.

Step 3: Check the Extruder

The extruder gear pulls filament from the spool and pushes it into the hotend. If it slips, you under-extrude.

Direct Drive Extruders (Bambu, modern Creality)

• Inspect the gear: Should grip filament with visible bite marks. Worn or smooth gears slip.
• Check tension: Most extruders have a tension lever or screw. Too loose = slipping. Too tight = grinding the filament flat.
• Clean the gear: Filament debris (especially from PLA-CF or wood-fill) packs into the gear teeth. Disassemble and clean with a brush.

Bowden Extruders (older Ender 3, etc.)

Add to the above:

• Check the Bowden tube: Should be free of kinks, smooth interior, and seated firmly in both ends.
• Replace if worn: Capricorn tubing ($10-15) has lower internal friction than stock PTFE.

Step 4: Check the Hotend

A partially clogged nozzle restricts flow. Common causes:

Burnt Filament Buildup

Old filament carbonizes inside the nozzle, partially blocking the path.

Fix: Cold pull (atomic pull):

1. Heat nozzle to printing temp
2. Manually push filament through (clears soft material)
3. Cool nozzle to 90°C (PLA) or 100°C (PETG)
4. Pull filament out forcefully — the cooled tip pulls debris out with it
5. Repeat 3-5 times until the pulled tip is clean

Foreign Material

Dust, hair, or contamination jamming the nozzle.

Fix: Hot needle clean:

1. Heat nozzle to printing temp
2. Insert a 0.4mm acupuncture needle through the nozzle (sold for 3D printer cleaning, $5)
3. Gently work it back and forth
4. Extrude filament to flush debris

Worn Nozzle

Brass nozzles wear from use, especially with abrasive filaments. Worn nozzles can develop irregular openings that cause inconsistent flow.

Fix: Replace the nozzle ($1-3 for brass, $20-30 for hardened steel). Takes 5 minutes.

For abrasive filament users (CF, glow-in-the-dark, wood-fill), a hardened steel nozzle is required. See Best Carbon Fiber 3D Printer for printers that ship hardened.

Step 5: Check Flow Rate (E-Steps)

Your printer’s extruder is calibrated to extrude X mm of filament per Y motor steps. If this is wrong, you’ll under-extrude even with everything else correct.

Calibrate E-Steps (Manual)

1. Mark filament 110mm above the extruder entry
2. Tell printer to extrude 100mm at slow speed (10mm/s)
3. Measure remaining distance — should be 10mm
4. If under-extruded (e.g., 15mm remaining), increase E-steps
5. Adjust formula: new_e_steps = current * (100 / actual_extruded)

Calibrate Flow Rate (Slicer)

In your slicer (Bambu Studio, Cura, OrcaSlicer), the flow rate is a global multiplier. Default is 100%. If you’re consistently slightly under-extruding after E-step calibration, increase to 102-105%.

Bambu printers auto-calibrate flow per filament — let it run on first use.

Step 6: Slow Down

If your printer simply can’t extrude fast enough, the answer is to print slower.

Volumetric flow rate = nozzle diameter × layer height × line width × speed.

Standard 0.4mm nozzle: max ~12mm³/s for PLA. Bambu’s enhanced hotend: ~25mm³/s.

If you’re trying to print at 500mm/s with 0.2mm layers, you’re asking for ~24mm³/s — beyond most stock hotends. Either slow down or upgrade to a high-flow hotend.

When to Suspect Hardware Failure

If you’ve worked through every fix above and still see under-extrusion, suspect:

• Bad thermistor — reports incorrect temperature, hotend isn’t actually at the temp it claims
• Failing heater cartridge — can’t maintain temp under flow
• Hotend leak — filament leaks at the heat block / nozzle joint, reducing pressure

These require part replacement ($5-20 each) but solve persistent under-extrusion that nothing else fixes.

Related Issues

• How to Fix Stringing — opposite problem (over-flow at travel)
• How to Fix Z-Banding — different visual but can have similar root causes
• Best Filament Dryer — wet filament fix