How to Fix 3D Printer Under-Extrusion (7 Causes & Fixes)

Under-extrusion is one of the most frustrating 3D printing problems. Your printer is running, filament is moving — but your prints come out weak, gappy, or stringy. The layers don't bond properly, walls are thin, and surfaces look rough or porous.

The good news: under-extrusion almost always has a specific, fixable cause. This guide walks you through all 7 common culprits and how to fix each one. We fix under-extrusion issues every week at Forgely Roy in Roy, Utah — here's exactly what we check.

What Is Under-Extrusion?

Under-extrusion happens when your printer deposits less filament than intended. The extruder stepper motor is commanded to push a certain amount of filament, but less actually makes it to the nozzle. The result: thin walls, layer gaps, poor layer adhesion, and weak prints that snap easily.

Signs You Have Under-Extrusion

• Gaps between infill lines
• Thin or incomplete perimeter walls
• Layers that don't fully bond (visible Z-gaps)
• Prints that snap or crumble under light pressure
• Extruder motor clicking or skipping
• Rough, porous surface texture
• Partial layer dropouts (one layer prints fine, the next has gaps)

If your extruder is skipping (clicking repeatedly), that's a strong indicator the motor can't push fast enough — usually a partial clog, temperature issue, or too-high print speed.

The 7 Most Common Causes of Under-Extrusion

1. Partial Nozzle Clog

The #1 cause of under-extrusion. A partial blockage lets some filament through, but not enough. Unlike a full clog (where nothing comes out), a partial clog allows printing to continue — just at reduced volume.

Signs: Inconsistent extrusion, extruder skipping, prints fine at first then degrades mid-print.

Fix:

• Cold pull (atomic pull): Heat to print temp, let cool to 90–100°C (PLA) or 140–160°C (PETG/ABS), then pull the filament out firmly. Repeat until the tip comes out clean with a perfect cone shape.
• Heat-and-purge: Try printing 10–15°C hotter to melt trapped residue. Purge 50–100mm of filament.
• Nozzle cleaning needle: Insert a 0.4mm cleaning needle at print temperature to break up partial blockages.
• If none of these work, replace the nozzle — they're $2–5 and often the fastest fix. See our full clogged nozzle guide.

2. Print Temperature Too Low

Filament that isn't fully melted can't flow fast enough through the nozzle. This is especially common with materials like PETG, ABS, and Nylon that need higher temps, or when printing at high speeds.

Fix: Increase nozzle temperature by 5°C increments. For PLA, try 210–220°C if you're currently at 200°C. For PETG, 230–245°C. Run a temperature tower test to find your material's ideal temp.

Warning: Don't exceed the filament manufacturer's max recommended temp — you'll risk carbonization inside the hotend.

3. Print Speed Too High

Your hotend can only melt filament so fast. If you push filament through faster than it can melt, you get under-extrusion — especially in large infill areas where speed tends to spike.

Fix:

• Reduce print speed by 20–30% and test
• Check your slicer's max volumetric speed setting (or enable it)
• For Bambu Lab: check per-material volumetric speed caps in filament profile
• Typical max volumetric: PLA standard ~15 mm³/s, high-speed PLA up to 30+, PETG ~10–12 mm³/s

4. Extruder Tension Too Low (or Too High)

The extruder gear needs enough tension to grip the filament without grinding through it. Too loose = filament slips, too tight = filament gets ground down into dust.

Signs of slipping: Extruder motor spins but filament doesn't advance; you can hear the motor turning without resistance.

Signs of over-tension: Filament dust or shavings near the extruder; filament looks chewed up.

Fix:

• Most extruders have a tension adjustment screw or spring. Start at middle tension and test.
• Visually inspect the filament coming out of the extruder — look for grinding marks.
• BMG-style and Orbiter extruders have click-adjust tension — set to manufacturer spec.

5. Bowden Tube Damage or Gap

In Bowden-style printers (Ender 3, most budget printers), the PTFE tube connects the extruder to the hotend. If this tube is worn, has a gap at the coupler, or has developed a gap inside the hotend, filament can get stuck or create a jam zone.

Signs: Under-extrusion that gets worse over time; filament blobs forming at the coupler fitting; difficulty loading filament.

Fix:

• Push the bowden tube all the way into the hotend fitting while hot — it seats better when the coupler is warm.
• Inspect the tube end for deformation or burning. Capricorn PTFE tubing ($10–15) lasts 3× longer than stock.
• Check that the tube creates a zero-gap connection to the nozzle inside the hotend. Even a 1mm gap causes a melt chamber and eventual clog.

6. Wet / Moisture-Damaged Filament

Filament absorbs moisture from the air. Wet filament doesn't extrude consistently — you'll hear popping, crackling, and hissing sounds during printing. The steam created by moisture in the melt zone disrupts flow and causes under-extrusion.

Moisture-sensitive materials (worst to mildest): Nylon > PA-CF > TPU > PETG > PLA+/PLA

Signs: Popping or crackling while printing; bubbly, rough surface; increased stringing; filament snaps easily when bent.

Fix:

• Dry the filament: Food dehydrator at 45°C for 4–8 hours (PLA) or 65°C for 6–12 hours (Nylon, PA-CF). Or use a dedicated filament dryer like the eSun eBOX.
• Store filament in sealed bags with silica gel desiccant. See our filament storage guide →
• For PETG, Nylon, and TPU — always store sealed. Once wet, they need drying before every print.

7. Flow Rate / Extrusion Multiplier Set Too Low

The extrusion multiplier (also called flow rate or extrusion factor) in your slicer directly scales how much filament is pushed. If it's set below 100% — or if it was set lower by mistake — you'll consistently under-extrude.

Fix:

• In Bambu Studio: check Filament → Flow Ratio (should be ~0.95–1.0 for PLA, ~0.98 for PETG)
• In OrcaSlicer/Prusa Slicer: Filament → Extrusion Multiplier
• In Cura: Material → Flow (should be 100%)
• Run an extrusion calibration (single-wall cube) to find the correct multiplier for each filament.

Diagnosing Under-Extrusion Systematically

Not sure which cause you have? Work through this checklist in order — faster fixes first:

1. ✅ Check slicer flow rate — is it at 100%?
2. ✅ Try increasing temperature by 5°C and test
3. ✅ Reduce print speed by 25% and test
4. ✅ Inspect and dry your filament
5. ✅ Check extruder tension — look for filament dust
6. ✅ Do a cold pull to clear any partial clog
7. ✅ Check bowden tube seating and condition
8. ✅ Replace nozzle if clog persists

If you've gone through this entire list and still have under-extrusion, it's likely a hardware issue — worn extruder gears, heat break problems, or a damaged hotend assembly. That's when it's time to bring it in.

When Under-Extrusion Is a Hardware Problem

Some under-extrusion causes require physical inspection and parts replacement:

• Worn extruder gears — The teeth wear down over time, especially with abrasive filaments. The gear looks fine visually but can no longer grip properly. Replacement is straightforward and parts are cheap ($5–15).
• Damaged heat break — A cracked or deformed heat break causes a melt zone above the hotend, leading to jams and under-extrusion that no cleaning will fix.
• Heater block issues — Loose heater cartridge or thermistor means temperature readings are wrong, causing intermittent under-extrusion.
• Clogged hotend assembly — Full hotend replacement is sometimes faster than trying to save a heavily clogged assembly.

Under-Extrusion by Printer Brand

Some printers have known under-extrusion tendencies:

Bambu Lab (X1C, P1P, P1S, A1)

Under-extrusion on Bambu printers is usually caused by AMS filament feed issues (tangles, empty spool, filament runout sensor error) or nozzle clogging from switching materials without purging. Check AMS hub buffer for kinks. Run the nozzle purge sequence before switching materials.

Creality Ender 3 / CR-10 Series

The Ender 3's stock extruder arm is plastic and cracks easily — the #1 cause of under-extrusion on this platform. Upgrade to an all-metal extruder ($15–25) as a first step. Also check bowden coupler — stock couplers loosen over time and create tube gaps.

Prusa MK4 / MK3S+

Prusa's Nextruder (MK4) is more reliable, but under-extrusion can occur with incorrect input shaper calibration after firmware updates. Run the resonance test. On MK3S+, check bondtech gear hex screws — they loosen and cause slip.

Summary

Under-extrusion is fixable — in most cases with just a slicer tweak or a cold pull. Start simple (temp, speed, flow rate) before assuming hardware failure. When it is hardware, the most common culprits are a partial nozzle clog, worn extruder gears, or a bad bowden tube connection.

Still stuck? Our techs at Forgely Roy have seen every under-extrusion scenario. Drop off your printer and we'll figure it out. Walk-ins welcome Mon–Fri 11–6, Sat 11–3.

📍 Forgely Roy — 5519 S 1900 W, Roy, UT 84067
📞 385-449-2694
🔧 See all repair services →