How to Fix Stringing, Blobs, and Oozing in 3D Prints: The Complete Troubleshooting Guide
Understanding the Root Causes
Stringing, blobs, and oozing are all symptoms of molten plastic being where it shouldn't be. But they have different root causes, and fixing one incorrectly can make another worse.
- Stringing — thin wisps of plastic between separate parts of a print, caused by molten filament leaking from the nozzle during travel moves
- Blobs — small bumps on the surface, usually at layer change points or where the nozzle pauses, caused by pressure buildup in the nozzle
- Oozing — general term for uncontrolled filament flow, the underlying cause of both stringing and blobs
The fundamental problem is nozzle pressure. When the extruder pushes filament, pressure builds up in the melt zone. When the extruder stops pushing (during travel moves or retractions), that residual pressure continues to push molten plastic out of the nozzle [1]. Different slicer settings control this pressure in different ways.
Fix #1: Retraction Settings
Retraction is your primary weapon against stringing. When the extruder retracts, it pulls filament backward, creating negative pressure that sucks the molten tip back into the nozzle.
The two key parameters are retraction distance and retraction speed.
| Extruder Type | Retraction Distance | Retraction Speed |
|---|---|---|
| Direct Drive | 0.5–2.0mm [1] | 25–45mm/s |
| Bowden | 3.0–7.0mm [1] | 40–60mm/s |
| Bambu Lab (Direct) | 0.5–1.5mm [2] | 30–40mm/s |
Start at the low end and increase until stringing stops. Too much retraction causes its own problems — grinding the filament, creating gaps at restart points, or causing heat creep in all-metal hotends.
Retraction Distance
Direct drive extruders need very short retraction (0.5–2mm) because the filament path from gear to melt zone is short [1]. Bowden extruders need 3–7mm because the long PTFE tube between the gear and hotend has compliance — the filament compresses and stretches in the tube, so you need more retraction to actually relieve nozzle pressure.
If you're above 2mm on direct drive or 7mm on Bowden and still stringing, retraction distance is not your problem — look at temperature and travel speed instead.
Retraction Speed
Retraction speed is how fast the extruder pulls back. Faster retraction relieves pressure more quickly, but going too fast can grind the filament (especially with soft materials like TPU) or cause the filament to skip on the extruder gear [1].
Sweet spot: 30–45mm/s for most setups. If you hear clicking during retraction, slow it down.
Fix #2: Temperature
Temperature is the second most impactful setting. Higher temperatures make filament more fluid, which means it flows more easily under residual nozzle pressure — causing more stringing and oozing.
If you're stringing after dialing in retraction, drop your nozzle temperature by 5°C increments. Stop when you start seeing under-extrusion or poor layer adhesion.
Typical temperature ranges where stringing is minimized:
| Material | Low-String Temp Range | Notes |
|---|---|---|
| PLA | 195–210°C [3] | Lower end of range strings less |
| PETG | 225–240°C [4] | PETG is inherently stringy; 230°C is often the sweet spot |
| ABS | 230–245°C [5] | Less stringy than PETG at proper temp |
| TPU | 210–230°C [6] | Very oozy; retraction often disabled entirely |
A temperature tower is the fastest way to find your filament's sweet spot. Print one column at varying temperatures and visually compare the bridging and stringing at each level.
Fix #3: Travel Speed and Settings
The faster your printhead moves between points, the less time there is for oozing to deposit strings. Increasing travel speed from 100mm/s to 150–200mm/s can significantly reduce stringing.
Related travel settings that help:
- Combing mode / "Avoid crossing perimeters" — forces travel moves to stay inside the print's boundaries, so any oozing happens inside the infill where it's invisible. This eliminates visible stringing at the cost of longer travel paths.
- Z-hop on retract — lifts the nozzle during travel moves. Helpful for preventing the nozzle from dragging across the surface, but can increase stringing because the lifted nozzle drips more freely. Try both with and without.
- Wipe distance — before retracting, the nozzle wipes along the last printed perimeter to clean the tip. Very effective for PETG and TPU. OrcaSlicer calls this "Wipe while retracting."
- Travel acceleration — higher acceleration means the nozzle reaches full travel speed faster, reducing the time spent at low speeds where oozing is worst.
Fix #4: Pressure Advance / Linear Advance
Pressure advance (called Linear Advance in Marlin firmware, Pressure Advance in Klipper) is a firmware feature that proactively manages nozzle pressure [7]. Instead of waiting for pressure to build up and then trying to relieve it with retraction, PA reduces extrusion pressure ahead of time during deceleration.
Properly tuned PA dramatically reduces blobs at corners and layer changes, and reduces the work that retraction has to do.
| Extruder Type | Typical PA Value |
|---|---|
| Direct Drive | 0.02–0.08 [7] |
| Bowden | 0.3–1.2 [7] |
| Bambu Lab | Usually pre-calibrated [2] |
Calibrate PA by printing a PA calibration pattern (available in OrcaSlicer and Klipper). Look for the line where corners are sharpest without gaps — that's your optimal value.
Filwiz's Pressure Advance Wizard generates printer-specific PA test G-code and helps you identify the optimal value.
Material-Specific Fixes
Different materials have different oozing behaviors and need different approaches.
PLA
PLA is the easiest material to de-string. It responds well to retraction and temperature reduction. Start at 200–205°C with 1mm retraction (direct drive) and adjust from there. PLA strings are thin and can often be removed with a heat gun or lighter.
If PLA is stringing badly, check for moisture first — wet PLA strings much more than dry PLA because steam creates additional pressure in the nozzle.
PETG
PETG is inherently stringy — it has a wide melt transition zone and stays fluid at lower temperatures [4]. You will likely never completely eliminate PETG stringing; the goal is to minimize it.
Best PETG-specific settings:
- Temperature: 225–235°C (lower end of range)
- Retraction: 1–2mm direct drive, 4–6mm Bowden
- Enable wipe/wipe on retract
- Combing mode ON ("Not in Skin" or "Within Infill")
- Slightly lower fan speed (50–70%) improves surface quality even if stringing increases marginally
ABS/ASA
ABS strings less than PETG but more than PLA. It responds well to retraction tuning. The enclosed chamber that ABS requires helps maintain consistent temperature, which actually reduces stringing vs. printing in open air.
Watch for blobs at layer changes — ABS is prone to pressure-related blobs, especially at slow speeds. Pressure advance helps significantly here.
TPU/Flexible
TPU is extremely oozy and soft, making retraction difficult or impossible. Many direct drive setups can handle 0.5–1mm of retraction with TPU, but Bowden setups generally cannot retract TPU at all because the filament compresses in the tube [6].
Fixes for TPU:
- Print as fast as reasonably possible (60–80mm/s on capable printers) to minimize travel time
- Disable retraction on Bowden setups; use 0.5–1mm max on direct drive
- Lower temperature to the lowest printable value
- Use combing mode aggressively
- Accept that some stringing will happen — clean up with a heat gun after printing
Blob-Specific Fixes
If your main problem is blobs rather than stringing, the cause is usually at the seam point (where each layer starts and ends) or at retraction restart points.
- Seam blobs — Set your slicer's seam position to "Aligned" or "Rear" so all seam blobs appear in one line that can be sanded. "Random" seam distributes blobs across the entire surface.
- Wipe and coast — Enable both. Coast stops extrusion slightly before the end of a perimeter, using residual pressure to fill the last bit. Wipe moves the nozzle back along the perimeter after stopping extrusion to clean the tip.
- Extra restart distance — If you see gaps after retractions (the opposite of blobs), increase the extra restart distance. If you see blobs after retractions, decrease it (or set it slightly negative).
- Linear advance / Pressure advance — The single best fix for blob-free prints. It proactively manages pressure changes, eliminating most blob causes at the firmware level [7].
Troubleshooting Checklist
Work through these fixes in order — each step builds on the previous:
- 1. Check for wet filament (listen for popping) → Dry if needed
- 2. Print a temperature tower → Use the lowest temperature that still has good adhesion
- 3. Print a retraction test → Increase retraction distance in 0.5mm increments
- 4. Increase travel speed to 150+ mm/s
- 5. Enable combing / avoid crossing perimeters
- 6. Enable wipe on retract
- 7. Calibrate pressure advance → Print PA calibration pattern
- 8. Adjust seam settings if blobs persist
- 9. If nothing works — try a different filament brand. Some budget filaments are simply too inconsistent to dial in.
Sources
- [1]E3D, "Retraction Settings Guide" — retraction distance and speed recommendations by extruder type. https://e3d-online.com/blogs/news/retraction-settings
- [2]Bambu Lab, "Filament Settings Guide for P1S and X1C" — recommended retraction and PA settings for Bambu printers. https://wiki.bambulab.com/en/filament-guide
- [3]NatureWorks, "Ingeo 4043D Technical Data Sheet" — PLA processing temperature range. https://www.natureworksllc.com/products/ingeo-biopolymer-4043d
- [4]Eastman Chemical, "Eastar 6763 PETG Processing Guide" — PETG extrusion temperature range and melt behavior. https://www.eastman.com/pages/producthome.aspx?product=71107096
- [5]SABIC, "Cycolac ABS Processing Guide" — ABS recommended processing temperatures. https://www.sabic.com/en/products/polymers/acrylonitrile-butadiene-styrene-abs
- [6]BASF, "Elastollan TPU Processing Guide" — TPU extrusion parameters and retraction limitations. https://plastics-rubber.basf.com/global/en/performance_polymers/products/elastollan.html
- [7]Klipper Documentation, "Pressure Advance" — how PA works and calibration methodology. https://www.klipper3d.org/Pressure_Advance.html