Start from the machine, not the filament
The Original Prusa MINI and MINI+ are Bowden printers, and that one fact decides the stringing fix: a Bowden tube needs a longer retraction than Prusa's direct-drive machines, so copying an MK3 setting onto a MINI makes the hairs worse instead of better. PETG only amplifies the problem, because it oozes more than PLA at the same temperature.
Why the MINI strings
Two things dominate, per the Prusa Knowledge Base stringing and oozing article: the nozzle temperature is too high, and/or the retraction settings do not match the machine. The MINI and MINI+ use a Bowden extruder, so they need a longer retraction than Prusa's direct-drive machines. Moist PETG makes it worse, so a dry spool is the first thing to rule out.
Retraction settings that matter
The numbers below come from the Prusa Knowledge Base stringing and oozing page.
- Retraction length — on the MINI/MINI+ the Bowden default is 3.2 mm (Printer Settings → Extruder 1). Do not copy the direct-drive value; it is far too short for a Bowden. (Prusa KB)
- Retraction speed — higher values reduce stringing, but too high can skip motor steps. (Prusa KB)
- Nozzle temperature — lower it 5–10 °C and re-test before changing anything else. (Prusa KB)
- Retract on layer change — keep it on. (Prusa KB)
- Minimum travel after retraction — the PrusaSlicer preset is 1 mm; raising it speeds up prints but increases oozing and stringing. (Prusa KB)
- Rule out moisture — a spool that has gathered moisture will string a lot, so Prusa suggests trying a different (dry) spool before changing settings further. (Prusa KB)
Checking the fix
Slice a small part with two separate squares 15 mm apart and watch the travel move between them. Adjust retraction length first, re-slice, and check the gap: when the hairs are gone and the squares still have solid perimeters, the Bowden value is right. If hairs remain, drop the nozzle in 5 °C steps before touching anything else, so you do not trade stringing for weak layer adhesion.