Stringing and oozing

Updated 2 weeks ago ​by Tomáš Chvalina

Stringing and nozzle oozing are the two most common printing problems that have same the same root cause. Very high printing temperatures and/or using incorrect retraction settings. Stringing usually appears when your print settings are not accurate and are printing complex objects (such as Moon city) or multiple objects at once. This is recognizable as a string of plastic left behind between the object/s. In other words, it’s that hairy bit of plastic we don’t like to see.

This can be solved by changing a couple of settings in PrusaSlicer. You should start by checking a parameter known as Retraction. What does retraction do? When the extruder has finished printing one section of your model, the filament is then pulled back into the nozzle.

Keep in mind that some filaments, such as PETG or flexible filaments, may be stringy even with perfect print settings.
Flexible filaments usually need longer retractions, because the material stretches while being pulled back to the nozzle. Flexible materials are a special case and need a lot of tweaking and tuning.


  1. Check the tension bolts – Before you touch any of the settings, make sure that the Tension bolts located on the extruder idler are properly tightened, although, this is not that common.
    1. Original Prusa i3 MK3: simply check STEP 17 in the MK3 E-axis assembly.
    2. Original Prusa i3 MK2/S: simply check STEP 16 in the MK2 Extruder assembly.
  2. Use proper printing settings – We highly recommend using the preset settings in PrusaSlicer. However, if you are printing with your own settings, make sure that you have the retraction settings set correctly. Retraction settings can be found in Printer Settings – Extruder 1.
Make sure the boxes for 'Retract on layer-change' and 'Wipe while retracting' are checked. Use correct value for retraction. Users often increase retraction to meaningless values, so check the PrusaSlicer settings and make sure that you have the retraction set to a maximum of 2 mm.

  1. Try to lower the nozzle temperature – Lowering the temperature will minimize stringing. Therefore, you can try to decrease it by 2-5°C. Do so only for materials which are experiencing strings, if you lower the temperature too much, the extruder can clog.
Stringing from material blob on the nozzle. If you print for a long time from a single type of filament, such as PET-G, the filament can create a thin layer in the nozzle. Therefore, thoroughly clean the nozzle before printing.
When changing type of material always load at the higher temperature. Example, When going from PETG to PLA, always load the PLA at PETG temperatures.

Don’t bother, just use a heat-gun! 

If you don’t feel like tweaking any of the settings, well, then there is an alternative. You can get rid of the strings with a heat gun (or possibly with a lighter). Just set it to around 200°C and aim at the strings for one or two seconds. This will melt the strings, and the printed object should remain undamaged.

If you do not have a heat-gun, a flash from a normal lighter will go a long way.


Find out more troubleshooting tips here: Community Forum | Assembly Manuals | Youtube channel |

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