Thin strings between parts of the print (stringing)

Symptom

Thin strands, like cobwebs or hairs, appear between separate areas of the part or between several parts on the same plate, right where the nozzle should only travel without extruding.

Likely causes, from most to least likely

1. Wet filament: moisture makes the molten plastic ooze and leave lots of strings.
2. Nozzle temperature too high for that filament: the plastic is very runny and drips during travel moves.
3. Retraction disabled or badly set (length or speed) for your extruder.
4. A film of material stuck to the nozzle after printing the same filament for a long time, especially PETG, which leaves strands on the part.
5. Materials that naturally tend to string, such as PETG.
6. Uncompensated nozzle pressure (pressure advance or linear advance not calibrated), which lets plastic ooze during travel.

Checks to tell which one it is

• Try another spool that is dry or freshly opened: if the strings almost disappear, moisture is the problem.
• When purging, check whether the filament bubbles or gives off smoke: that is a sign of moisture.
• Lower the nozzle temperature by 5-10 °C and compare: if it improves, you were printing too hot.
• Check in the slicer that retraction is enabled and its length doesn't exceed what your printer manufacturer recommends.
• Look at the nozzle tip while it is hot, without touching it: if there is residue stuck to it, clean it before changing anything else.

Before you start

Before taking anything apart, cleaning or adjusting it, switch the printer off and unplug it, unless a step says otherwise, and do not touch the nozzle, the heater block or the bed until they have cooled down. If in any doubt about electricity, heat or moving parts, stop and ask a professional.

Step-by-step fix

1. Dry the filament

   Dry the spool in a filament dryer or an oven with a reliable temperature, using the temperature and time given by the filament manufacturer. Then store it in a closed box or bag with desiccant.

   Check: When you reprint the same part, the strings are clearly reduced.

   If that does not fix it: Lower the nozzle temperature.

2. Lower the nozzle temperature

   Reduce the nozzle temperature by 5-10 °C (Prusa's guideline) without going outside the range recommended by the filament manufacturer.

   Check: There are fewer strings and the layers are still well bonded.

   If that does not fix it: If layers start to separate or the extruder clicks, go back to the previous temperature and adjust retraction.

3. Adjust retraction

   Enable retraction and keep its length within what your printer manufacturer recommends: Prusa, for example, sets a maximum of 2 mm on its MK2.5 and MK3, while Bowden extruders use longer retractions. A higher retraction speed helps, but if it is too high the motor skips steps. Also enable retract on layer change and wipe while retracting.

   Check: Strings between parts disappear or nearly so.

   If that does not fix it: Reduce travel outside the part.

4. Reduce travel outside the part

   In the slicer, enable avoid crossing perimeters and only retract when crossing perimeters, so the nozzle travels inside the part. With several parts, printing them one after another (sequential mode) reduces strings between them.

   Check: There are fewer strings on the outside of the part.

   If that does not fix it: Clean the nozzle.

5. Clean the nozzle

   Before printing, clean the nozzle thoroughly and remove dirt and leftovers from previous filaments. Take care: a hot nozzle burns.

   Check: The tip is clean and strings no longer catch on the part.

   If that does not fix it: Calibrate pressure advance or linear advance if your firmware has it.

6. Calibrate pressure advance or linear advance

   If your firmware supports it (pressure advance in Klipper, linear advance in Marlin), calibrate it for each filament. Once pressure advance is tuned, the Klipper documentation suggests a small retraction (for example 0.75 mm) and using wipe on retract.

   Check: Less oozing at the end of lines and during travel moves.

   If that does not fix it: For any remaining strings, pass a heat gun over them very briefly; overdo it and the part will deform.

Prevention

• Keep filament in a closed box or bag with desiccant and dry it if it has been left out.
• Start from the slicer's material profiles and change one setting at a time.
• Clean the nozzle when switching materials.

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Printers it applies to

Any FDM (filament) 3D printer, from any brand.

Official sources

This guide summarises the official documentation linked here:

• Stringing and oozing · Prusa Research
• Drying filament · Prusa Research
• PETG · Prusa Research
• Pressure advance · Klipper