Stringing and Oozing: Causes and How to Tune Retraction

Stringing is the fine web of plastic threads that bridges the gaps in a print — most visible between two separate towers or across the openings in a model. It happens because molten filament keeps flowing out of the nozzle during travel moves, when the printhead is moving but shouldn’t be extruding. The fix is to stop that flow, and there are several levers for doing it. The trick is pulling them in the right order.

Most people start by cranking retraction distance way up. That’s the wrong first move. Retraction is usually the third thing to fix, not the first.

Why Filament Oozes During Travel

A hot nozzle full of molten plastic is under pressure. When the printhead lifts and moves to a new location without extruding, that pressure keeps pushing material out — the nozzle dribbles a thin strand as it travels. Retraction fights this by physically pulling filament back to relieve the pressure before the move. But retraction can’t fix ooze that comes from other sources, which is why settings-only approaches often fail.

There are really three independent contributors:

1. Temperature too high — runnier plastic oozes more.
2. Wet filament — moisture flashes to steam in the hot end and forces material out, regardless of retraction.
3. Retraction not tuned — not enough pressure relief, or too slow.

Address them in that order.

Step 0: Rule Out Wet Filament

This is the one people skip, and it’s often the actual cause — especially with PETG and TPU, which absorb moisture quickly. Wet filament oozes from positive pressure that no retraction setting can defeat. The tell-tale signs: faint popping or hissing from the nozzle during printing, a rough or bubbly surface, and stringing that appears suddenly on a spool that printed cleanly a week ago.

PETG can pull in enough water over a single humid weekend to start stringing. If you suspect moisture, dry the spool before changing any settings — otherwise you’ll chase your tail tuning retraction against a problem retraction can’t solve. See our filament drying guidance ↗ for the materials most prone to it.

Step 1: Lower the Temperature

Hotter filament is runnier and strings more. Drop the nozzle temperature in 5C increments and watch the strings shrink. There’s a floor — go too low and you get poor layer adhesion, under-extrusion, or clogs — so you’re looking for the lowest temperature that still gives clean layers.

This is exactly what a temperature tower finds for you in a single print: bands at descending temperatures, with the stringing visibly worse at the top. Our temperature and flow calibration guide ↗ covers running one. PETG is especially temperature-sensitive for stringing; it prints well across roughly 230-250C, and the bottom of that band usually strings far less than the top.

Step 2: Tune Retraction Distance

Now the retraction itself. The right distance depends heavily on your extruder type, because the two designs behave completely differently:

• Direct drive (extruder motor on the printhead): short retractions. Start around 0.5-2mm. The filament path is short, so a little movement relieves a lot of pressure.
• Bowden (motor remote, filament fed through a tube): long retractions. Start around 4-6mm. The tube compresses and absorbs movement, so you need more travel to actually move the filament tip.

Change distance in 0.5mm steps and reprint a stringing test. More is not always better — over-retracting on direct drive can grind the filament or pull molten plastic back into the heat break and cause jams.

For flexible filament like TPU, keep retraction very short — around 0.5-1.5mm even on direct drive. Pull back further and the rubbery filament stretches instead of retracting, then springs forward and over-extrudes when the move ends.

Step 3: Tune Retraction Speed

Speed matters as much as distance. Retraction that’s too slow lets the nozzle keep dribbling during the pull-back itself. Start around 25 mm/s and work up; many printers do well in the 30-60 mm/s range. Too fast and you risk grinding a flat spot into the filament, so increase gradually and watch the extruder for skipping.

Step 4: Increase Travel Speed

The longer the nozzle hovers over open space, the more time it has to ooze. Faster travel moves cut that window. Most printers can safely run travel at 150-200 mm/s, which noticeably reduces stringing without any retraction change. This is a free improvement on most modern hardware.

Step 5: Slicer Combing and Wipe

Two more settings worth knowing:

• Combing / avoid crossing perimeters: keeps travel moves inside the part where strings won’t show on the visible surface. It doesn’t eliminate ooze, it just hides it.
• Wipe on retract / coast: the nozzle wipes along the last printed line as it retracts, depositing the oozed material where it won’t string. Small effect, but it cleans up the last bit.

A Sane Tuning Order

Run a stringing test print (a pair of bare towers is the classic) and change one variable at a time:

1. Confirm the filament is dry. If in doubt, dry it.
2. Drop temperature in 5C steps until adhesion starts to suffer, then back up one step.
3. Set retraction distance for your extruder type (short for direct, long for Bowden) and tune in 0.5mm steps.
4. Set retraction speed around 25 mm/s and raise it.
5. Raise travel speed.
6. Enable combing and wipe for the final cleanup.

A Note on PETG

PETG strings more than PLA, and that’s partly just the material — its higher viscosity and surface adhesion make ooze-free travel genuinely harder. You can get PETG very clean with the steps above, but expect a little light stringing that brushes off easily, rather than the near-perfect travel moves PLA gives you. Don’t chase perfection by over-retracting; you’ll trade strings for jams. Dry filament plus a temperature on the low side of the range does most of the work.

For more context, Bambu Lab printer reviews ↗ covers related topics in depth.