How to Stop PETG Stringing

PETG strings easily. Prusa lists "possibility of stringing" among the cons of PETG in its material guide, so thin hairs between parts are a normal complaint rather than a sign of a faulty printer. The fix is to make the melt less runny, stop it leaking during travel moves, and keep the plastic dry.

Symptoms and the usual cause

1. Dry the spool

Bambu Lab's wiki says moisture vaporizes in the hot nozzle, causing the molten material to burst and flow abnormally. Prusa makes the same point and suggests trying a different spool to see whether the filament is the problem. Follow the drying temperature and time printed on the spool or the maker's guidance. Our guide to drying filament covers the general method, and storing it sealed with desiccant keeps it dry afterwards.

2. Lower the nozzle temperature

Prusa says lowering the temperature decreases the occurrence of strings and suggests dropping the nozzle temperature by 5 to 10 degrees C and checking whether stringing improves. For reference, Prusa's PETG page lists 230 degrees C for the first layer and 240 degrees C for the other layers as recommended settings, though its own slicer profiles for specific Prusament PETG may differ. Check the range printed on your spool, and stay inside it. Going too cold risks weak layers and under-extrusion. See PETG print temperature for more on choosing a starting point.

3. Tune retraction

Retraction pulls filament back before a travel move so it does not leak across the gap. Prusa explains the main settings: retraction length, retraction speed and minimum travel after retraction. Its notes include these limits:

• On the MK2.5 and MK3 family, keep retraction length at 2 mm or less.
• The MINI preset uses a longer 3.2 mm default because of its Bowden extruder.
• A higher retraction speed improves stringing, but too high can make the extruder motor skip steps.
• A larger minimum travel distance gives shorter print times but more oozing and stringing.

Bambu Lab recommends increasing retraction length or speed appropriately, and keeping length no greater than 2 mm because overly long retraction can cause clogging. For a deeper explanation of each setting, read retraction settings explained.

4. Shorten and simplify travel moves

Fewer and shorter travel moves leave less time for the nozzle to ooze. Both makers suggest the same slicer options:

• Enable the "avoid crossing perimeters" option (Prusa) or "avoid crossing wall" (Bambu Studio) so travel stays inside the part.
• Reduce the spacing between objects on the plate.
• Prusa also notes that printing objects one at a time (sequential printing) lowers the chance of strings between parts, but warns to watch the print closely for collisions.

5. Keep the part cooling fan working

Prusa's PETG guide says cooling the print keeps the model detailed and prevents stringing and oozing. Its suggested approach is to run the first few layers with the fan off to prevent deformation, then at around half power. If you want the strongest possible part, Prusa notes the fan can be turned off for better layer bonding, but that trades away the anti-stringing benefit.

6. Check the nozzle

Prusa warns that long runs of PETG can leave a thin layer inside the nozzle, which causes stringing as strands stick to the print. Clean the nozzle thoroughly, especially after switching materials. Bambu Lab adds that a worn nozzle should be replaced, and that a nozzle larger than the slicer profile assumes will push out too much plastic, so make sure the nozzle in the slicer matches the real one. If your hotend is the type Prusa describes, poor heat dissipation at the heatbreak can also contribute.

How to confirm the fix

Print a small test with two thin towers a few centimeters apart. Change one setting, print it again and compare. If the towers come out clean, print a model with more travel to confirm. If the problem persists across all of the above, the general advice in our general stringing guide may help.

The last resort

Prusa mentions a heat gun set to around 200 degrees C held on the strings for one or two seconds. Holding it longer can deform the part. Prevention through the steps above is neater and quicker.