Stringing (also called oozing or whiskers) happens when melted plastic keeps leaking out of the nozzle while the printhead moves between two places it is not printing. The plastic is under pressure inside the hot end, so unless the printer actively pulls it back, gravity and that pressure drag a thin thread across the gap.
Almost every case comes down to one of six things. They are ordered below by how often they turn out to be the cause, so work down the list and stop when the strings go. Change one thing at a time and reprint the same small test, or you will not know which change worked.
Retraction is the printer pulling filament backwards before a travel move, which drops the pressure at the nozzle so nothing leaks out. If the distance is too small, pressure stays high and the nozzle keeps oozing.
The right distance depends almost entirely on your extruder type. A direct drive extruder sits on the printhead and needs very little. A Bowden setup pushes filament down a long tube that flexes under pressure, so it needs far more to achieve the same effect.
Do not just set it as high as it goes. Too much retraction pulls molten plastic far back up the melt zone, where it cools and jams, and it grinds a flat spot into the filament. If you are past 7 mm on Bowden or 2 mm on direct drive and still stringing, the cause is further down this list.
Hotter plastic is thinner plastic, and thinner plastic runs out of the nozzle more easily. If you are printing at the top of your filament's range, you are making stringing much more likely for no benefit on most prints.
The fastest way to find the right number is a temperature tower: a test model that changes temperature every few millimetres so you can see the whole range on one print.
Some plastics pull moisture out of the air. When that filament hits the hot end the water flashes to steam inside the nozzle and blows plastic out, which strings badly and no amount of retraction tuning will fix.
You have wet filament if you hear popping or crackling while it prints, see faint steam at the nozzle, or the surface has come out rough and pitted alongside the strings.
Nylon is the extreme case. It absorbs enough moisture in a day on the bench to print badly, which is why it is usually printed straight out of a dryer.
The nozzle oozes over time, so the less time it spends crossing open space, the smaller the string. Speeding up travel is a free improvement that costs nothing in print quality, because nothing is being printed during a travel move.
Most slicers can route travel moves so they stay inside the walls of the model, where a string would be hidden or never form. This is usually called combing or "avoid crossing perimeters".
If you have worked through everything above and nothing changed at all, the problem is probably mechanical rather than a setting. A partly blocked nozzle, or a PTFE tube that has shrunk back and left a gap above the nozzle, both let plastic pool where retraction cannot reach it.
These are the baselines PrinterPilot uses as a known-good starting point. They are not the only correct values, but if your settings are a long way from these it is worth asking why.
| Filament | Nozzle | Retraction | Notes on stringing |
|---|---|---|---|
| PLA | 205 °C | 2 mm | The most forgiving. Stringing here usually means retraction is off or the nozzle is well over 215 °C. |
| PETG | 240 °C | 4 mm | Strings much more readily than PLA. Expect to tune retraction properly and to dry the spool. |
| ABS | 245 °C | 5 mm | Strings less than PETG, but needs an enclosure, which raises ambient temperature and makes oozing worse. |
| ASA | 250 °C | 5 mm | Behaves like ABS. Keep cooling minimal and let retraction do the work. |
| TPU | 225 °C | 1 mm | Flexible filament compresses instead of retracting. Strings badly on Bowden setups; print slowly, 20–30 mm/s. |
| Nylon | 255 °C | 3 mm | Dry it first, every time. Wet nylon will string no matter what else you change. |
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