Stringing and oozing: rule out wet filament, then tune temperature and retraction
Short answer
Stringing is molten plastic leaking from the nozzle during travel moves. Bambu Lab and Prusa both name damp filament, an overly hot nozzle and unsuitable retraction as the main causes [1, 2]. Dry or swap the spool first, then try a nozzle 5–10 °C cooler [2], then print a retraction tower [3]. Bambu Lab advises keeping retraction length at or below 2 mm, because longer retractions can cause clogs [1].
Two related defects
Bambu Lab separates the two terms. Stringing is the thin, cobweb-like strands left on the surface or between parts when molten plastic seeps out during travel moves. Oozing is plastic that keeps leaking when the nozzle should not be extruding, which leaves local blobs, buildup on the nozzle and surface marks [1]. Both come from the same short list: too much material at the nozzle, damp filament and unsuitable retraction [1]. The Prusa Knowledge Base names very high printing temperature and incorrect retraction settings as the main triggers [2].
Symptom, likely cause, what to check
| Symptom | Likely cause | What to check |
|---|---|---|
| Strings plus popping or crackling sounds, rough or bubbly surface | Moisture in the filament | Dry the spool; Bambu Lab lists these sounds as a moisture sign [8] |
| Strings only between parts spaced far apart | Long travel with too little retraction | Part spacing, retraction length and speed [1] |
| Fine hairs everywhere, soft or droopy details | Nozzle temperature too high | Temperature tower; lower temperatures usually string less [5] |
| A retraction tower still strings at the top | Wet filament or a leaking nozzle | Dry the filament; check the nozzle is installed without leaks [3] |
| Heavy oozing with PLA Aero or other low-density filament | Gas and moisture expanding in the melt | Dry it, lower the temperature, set flow ratio 0.5–0.7 [1] |
| Stringing began after a nozzle swap or long service | Wrong nozzle in the profile, or a worn nozzle | Match the slicer nozzle to the installed one; replace a worn nozzle [1] |
| Strands sticking to the print after long PETG runs | Residue layer on the nozzle | Clean the nozzle before printing [2] |
| Stringing started after hotend maintenance | Poor heat dissipation or a misassembled part | Thermal paste on the heatbreak threads; compare the assembly with the manual [2] |
Diagnostic order
Work from causes that affect every print toward per-filament tuning. Retraction tuned on a wet spool stops being valid once the spool is dried.
- Rule out moisture. Prusa suggests trying a different spool first, since filament that has gathered moisture strings heavily [2]. Bambu Lab recommends drying before printing and printing from a sealed container with desiccant [1]. Product-specific drying settings are on the drying chart, and the wet filament guide lists the other symptoms.
- Confirm the nozzle. Check that the nozzle selected in the slicer matches the installed one and that the tip is not worn [1].
- Lower the temperature. Prusa suggests 5–10 °C lower as a first test [2]. OrcaSlicer’s temperature tower guide describes the trade-off: lower temperatures typically reduce stringing, but too low brings under-extrusion and poor layer adhesion [5]. See temperature tower calibration.
- Print a retraction tower. OrcaSlicer’s test defaults to 0–2 mm in 0.1 mm steps for direct-drive extruders and suggests 1–6 mm in 0.2 mm steps for Bowden setups. The right value is the shortest length that prints a clean section [3]. The method is covered in retraction calibration.
- Shorten and hide travel. Reduce the spacing between parts on the plate and enable Bambu Studio’s Avoid crossing wall option [1].
- Recheck retraction after pressure advance. Enabling or retuning pressure advance changes how much retraction is needed (see below).
Retraction limits
Longer is not automatically better. Bambu Lab generally recommends no more than 2 mm of retraction because longer settings can cause clogging [1], and OrcaSlicer’s documentation ties an overlong retraction to clogs or under-extrusion [4]. Prusa gives 2 mm as the maximum for the MK2.5/S and MK3/S/+, while the Bowden-fed MINI/MINI+ presets default to 3.2 mm [2].
Materials differ. OrcaSlicer notes that PETG and TPU string more readily and may need longer retractions than PLA or ABS, set per filament through a setting override [4]. For PLA or ABS whose tower is clean from the start, 0.2–0.4 mm can be enough [3]. Flexible filament stretches as it is pulled back, so Prusa expects longer retractions and more tuning [2].
Speed matters too: a faster retraction reduces stringing, but too fast can make the extruder motor skip steps [2].
Travel settings that limit exposed travel
| Effect | OrcaSlicer setting | PrusaSlicer setting | What the docs say |
|---|---|---|---|
| Detours around walls instead of crossing them | Avoid crossing walls | Avoid crossing perimeters | Reduces stringing, notably with PETG and TPU, at a small time cost [6, 2] |
| Moves the nozzle along the last path while retracting | Wipe while retracting | Wipe while retracting | Cleans leaked material and minimizes blobs [4]; Prusa recommends leaving it on [2] |
| Skips retraction on short moves | Travel distance threshold | Minimum travel after retraction | PrusaSlicer’s preset is 1 mm; a higher value saves time but increases stringing [2] |
| Retracts at every layer change | Retract on layer change | Retract on layer change | Prusa recommends leaving it on [2] |
| Lifts the nozzle during travel | Z-hop height, Z-hop type | Lift Z | Prusa: less lift reduces stringing but removing it risks collisions; OrcaSlicer: Spiral lift can help [2, 7] |
Pressure advance changes the retraction you need
Pressure advance (Klipper pressure_advance) and Linear Advance (Marlin M900 K) manage nozzle pressure as the toolhead accelerates and decelerates. Klipper’s documentation says pressure advance reduces ooze during non-extrude moves. Once it is tuned, a small slicer retraction (its example is 0.75 mm) plus wipe-on-retract may still help against ooze caused by filament cohesion, and Klipper recommends disabling z-lift on retract [10]. Marlin’s Linear Advance guide says to recheck retraction after calibration, because it may drop as low as 0, and to disable wipe-while-retract and similar pressure options, which interfere with Linear Advance [11].
The two firmware projects disagree on wiping. They agree that a retraction value tuned before pressure advance should be retested afterward. See pressure advance calibration.
Removing strings after printing
Prusa describes aiming a heat gun set to around 200 °C at the strings for one or two seconds; holding it longer can deform the part [2]. Bambu Lab lists hot air from a heat gun or hair dryer, or a quick pass of a lighter flame [9].
Safety: a heat gun and an open flame are burn and fire hazards, and Bambu Lab’s guide calls for careful operation with attention to safety for both methods [9].
Questions
Why does PETG string more than PLA?
OrcaSlicer's documentation lists PETG and TPU as more prone to stringing and notes they may need longer retractions than PLA or ABS [4]. Prusa's PETG guide adds that strong part cooling, higher retraction and a lower nozzle temperature help, and recommends starting from the stock PrusaSlicer profiles [12].
Does a longer retraction always reduce stringing?
No. Bambu Lab recommends staying at or below 2 mm because longer retractions can clog the nozzle [1], and OrcaSlicer's retraction test selects the shortest length that prints a clean section [3].
Is some stringing normal with TPU?
Bambu Lab states that TPU stringing cannot be avoided completely, especially on models with many travel moves; drying the spool and keeping it sealed with desiccant still reduces it [9].
Sources
- Stringing and Oozing. Bambu Lab Wiki. Manufacturer documentation. Definitions, six causes, 2 mm retraction guidance, flow ratio 0.5–0.7 for low-density filament. Accessed October 12, 2026.
- Stringing and oozing. Prusa Knowledge Base. Manufacturer documentation. PrusaSlicer retraction and travel settings, 5–10 °C temperature drop, heat-gun cleanup. Accessed October 12, 2026.
- Retraction test. OrcaSlicer Wiki. Slicer documentation. Retraction tower ranges for direct drive and Bowden; persistent strings point to wet filament or leaks. Accessed October 12, 2026.
- Retraction (printer extruder settings). OrcaSlicer Wiki. Slicer documentation. Retraction length, wipe, travel distance threshold; PETG and TPU string more. Accessed October 12, 2026.
- Temp Calibration. OrcaSlicer Wiki. Slicer documentation. Lower temperature reduces stringing; too low causes under-extrusion and weak adhesion. Accessed October 12, 2026.
- Walls and surfaces (Avoid crossing walls). OrcaSlicer Wiki. Slicer documentation. Avoid crossing walls reduces stringing, especially with PETG or TPU. Accessed October 12, 2026.
- Z Hop. OrcaSlicer Wiki. Slicer documentation. Z-hop types; spiral lift can reduce stringing. Accessed October 12, 2026.
- Model Warping, Falling Off, or Collapsing. Bambu Lab Wiki. Manufacturer documentation. Crackling or popping sounds and stringy surfaces as signs of moisture. Accessed October 12, 2026.
- Work After Printing Finished. Bambu Lab Wiki. Manufacturer documentation. TPU stringing cannot be fully avoided; removing strings with heat. Accessed October 12, 2026.
- Pressure advance. Klipper documentation. Firmware documentation. Pressure advance reduces ooze; small retract and wipe after tuning; disable z-lift. Accessed October 12, 2026.
- Linear Advance. Marlin Firmware documentation. Firmware documentation. Recheck retraction after calibration, possibly down to 0; disable wipe while retract. Accessed October 12, 2026.
- PETG. Prusa Knowledge Base. Manufacturer documentation. PETG stringing: cooling, retraction and temperature advice. Accessed October 12, 2026.