Why prints string
Stringing is the thin wisps of plastic left between separate parts of a print when the nozzle travels across open space. Prusa says it is caused by very high printing temperatures, incorrect retraction settings, or both [1]. Prusa lists three other causes. Residue can build up in the nozzle after long runs of a material such as PETG. Moist filament causes a lot of stringing. Heat may not leave the hotend properly, sometimes because parts were reassembled wrongly after a repair [1].
Some materials string more than others. Prusa calls PETG prone to stringing [3]. It says PLA is sometimes prone to stringing and oozing, and that proper retraction settings reduce it [4]. Some PETG wisps are normal. A PLA print that suddenly strings badly points to a change: a new spool, a new profile or a damp room.
Change one thing at a time and print the same small test after each change. If you change three settings and the strings go away, you will not know which change fixed it.
Step 1: retraction and travel settings
Start from your slicer's official profile for your printer and filament. Prusa recommends its own PrusaSlicer presets, or checking that your custom retraction settings are correct [1]. Retraction length depends on the extruder. Prusa keeps it at 2 mm or less on its MK2.5 and MK3 direct-drive printers, but uses a longer 3.2 mm default on the Bowden-fed MINI [1]. Copying a Bowden number onto a direct-drive printer, or the other way round, is a common way to make stringing worse.
| Setting (PrusaSlicer name) | Change that reduces stringing | Trade-off Prusa notes |
|---|---|---|
| Retraction length | Keep at the profile value; 2 mm or less on Prusa MK2.5/MK3, 3.2 mm on MINI [1] | Right value depends on direct-drive or Bowden extruder [1] |
| Retraction speed | Higher [1] | Too high and the extruder motor may skip steps [1] |
| Lift Z | Lower [1] | Disabling it can let the nozzle hit the printed part [1] |
| Minimum travel after retraction | Keep at the 1 mm preset [1] | A higher value saves time but increases oozing and stringing [1] |
| Retract on layer change; wipe while retracting | Keep both enabled [1] | None noted |
| Only retract when crossing perimeters | Enable (Print settings > Infill > Advanced) [1] | Oozing inside the walls is hidden rather than removed [1] |
| Avoid crossing perimeters | Enable (Print settings > Layers and perimeters > Quality) [1] | Prusa says it helps most on the MINI [1] |
| Sequential printing | Print several objects one at a time [1] | Watch for collision warnings in PrusaSlicer [1] |
Step 2: nozzle temperature
If the profile's retraction settings still leave strings, Prusa's next step is to lower the nozzle temperature by 5 to 10 °C and check whether stringing decreases [1]. For PETG, Prusa says higher retraction and a lower nozzle temperature moderate stringing, and that cooling the print helps prevent stringing and oozing [3].
The starting temperatures below are Prusa's figures for its own filaments. Another brand's spool label takes priority over this table. Go lower only until layers stop bonding well, then go back up a step.
| Material | Prusa nozzle temperature | Prusa bed temperature | Stringing note |
|---|---|---|---|
| PLA | 215 °C first layer, 210 °C after [4] | 60 °C [4] | Sometimes prone; reduce with retraction [4] |
| PETG | 230 °C first layer, 240 °C after [3] | 85 °C first layer, 90 °C after [3] | Prone to stringing; higher retraction, lower temperature, good cooling [3] |
Step 3: rule out wet filament
Prusa says filament that has absorbed moisture causes a lot of stringing, and suggests changing spools to test whether the filament is the cause [1]. A quick check is to load a spool you know prints cleanly. If the strings disappear, the original spool is the problem, not your settings.
Prusa's drying guide lists other signs of wet filament: poor surface quality, weak layer adhesion, blobs, and bubbling or smoke from the nozzle during extrusion [2]. It names four ways to dry filament: a dedicated filament dryer, a home oven, a professional drying oven or a food dehydrator. It warns that home ovens often lack precise temperature control, so use an external thermometer [2].
Step 4: residue, hotend and clean-up
If settings and dry filament do not stop the stringing, Prusa points to the hardware. Clean the nozzle of leftover material from earlier filaments. Then check the hotend: re-apply thermal paste between the heatbreak and heatsink, and confirm it was assembled as the official instructions show [1].
For a finished print, Prusa describes a heat-gun clean-up. Set the gun to about 200 °C and aim it at the strings for one or two seconds. Holding heat on the part longer can deform it [1].
Stringing checklist
- Print a small two-tower test with the slicer's stock profile and keep it as your baseline.
- Confirm retraction length matches your extruder type, direct drive or Bowden [1].
- Keep retract on layer change and wipe enabled; enable only-retract-when-crossing-perimeters and avoid-crossing-perimeters [1].
- Lower the nozzle temperature 5 to 10 °C and reprint the same test [1].
- Load a known-good spool. If the strings vanish, dry the original spool at the listed temperature [1][2].
- Clean nozzle residue, then check hotend assembly and thermal paste [1].
- If you also see clicking or partial extrusion, check for a partial clog as well; see the nozzle clog guide.
Questions before you decide
What retraction length should I use to stop stringing?
Use the value in your slicer's official profile first. Prusa keeps retraction at 2 mm or less on its MK2.5 and MK3 direct-drive printers and uses 3.2 mm on the Bowden-fed MINI, so the right figure depends on your extruder.
Does lowering the nozzle temperature reduce stringing?
Often, yes. Prusa suggests lowering the nozzle temperature by 5 to 10 °C and checking whether stringing decreases. For PETG it also recommends higher retraction and good part cooling.
Can wet filament cause stringing?
Yes. Prusa says moist filament causes a lot of stringing. Swap to a known-good spool to test. Prusa dries its PLA at 45 °C and PETG at 55 °C, both for 6 hours.
How do I remove strings from a finished print?
Prusa describes setting a heat gun to around 200 °C and aiming it at the strings for one or two seconds, without holding heat on the part long enough to deform it.
Sources & verification
Product details and prices can change. Check the linked provider before buying.
- Prusa Knowledge Base: Stringing and oozing Accessed 30 Oct 2026
- Prusa Knowledge Base: Drying filament Accessed 30 Oct 2026
- Prusa Knowledge Base: PETG material guide Accessed 30 Oct 2026
- Prusa Knowledge Base: PLA material guide Accessed 30 Oct 2026
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