3D print stringing vs. oozing: how to spot the difference and fix it

Stringing vs. oozing: one cause, two patterns

Stringing is the cobweb effect: thin hairs of plastic stretched between two features of a part, or between separate parts on the same plate. Simplify3D lumps stringing, oozing, whiskers and so-called hairy prints together and sums up the cause in one line: plastic leaks out of the nozzle while the extruder travels to a new spot. The Prusa Knowledge Base describes it the same way, as a line of filament left behind between objects.

For troubleshooting, though, it pays to split the problem in two. Travel stringing happens when the nozzle crosses open air, drags out a hair, and then prints normally once it lands. Continuous oozing is different: the melt is so runny, or the nozzle so dirty, that plastic escapes even on short moves and leaves residue stuck to the walls. Neither source draws that line as sharply, but their fixes fall neatly on either side of it. Travel stringing responds mainly to retraction and travel settings. Continuous oozing points you toward temperature, wet filament and the condition of your hotend.

Read the strings before you touch the slicer

Start by looking at where the hairs are. Clean, straight strings running between two towers or two islands on the same layer point to travel: the nozzle leaked while it crossed the gap. Simplify3D stresses that move length matters a lot. A short hop may be too quick for plastic to escape, while a long move over open space is far more likely to leave a string behind.

If the strings are messy, show up even on tiny moves, or come with small beads of plastic on the walls, continuous oozing becomes the better bet. Prusa lists several culprits of that kind: printing too hot, filament that has absorbed moisture, and a thin film of material left in the nozzle after long runs of PETG. Isolated surface dots are often a related defect covered in our guide to blobs and zits. Before changing anything, print a simple test with two separated towers. It isolates the problem and gives you a baseline to compare against after every tweak.

Retraction: distance, speed and when it fires

Retraction pulls filament back at the end of a section and pushes it forward again before printing resumes. Simplify3D calls distance the single most important setting. Most direct drive extruders need only 0.5 to 2 mm, while some Bowden setups may need as much as 15 mm because of the long path between the drive gear and the hot nozzle. The suggested method is straightforward: add 1 mm, reprint and compare. Prusa caps retraction at 2 mm on its MK2.5/S and MK3/S/+ printers.

Speed matters too. Retract too slowly and plastic oozes before the move is over. Retract too fast and the filament can separate from the melt or get chewed up by the drive gear. Simplify3D puts the sweet spot somewhere between 20 and 100 mm/s. In PrusaSlicer, also check the minimum travel that triggers a retraction. The preset is 1 mm, and raising it shortens print time but increases stringing. Keep retract on layer change and wipe while retracting turned on. Our retraction settings guide walks through each parameter in detail.

Nozzle temperature: step it down in small increments

Once retraction checks out, Simplify3D names extruder temperature as the next most common cause. Hotter plastic is less viscous, so it leaks out of the nozzle more easily, even after a retraction. Both sources give the same starting point: drop your nozzle temperature by 5 to 10 °C and compare the result against your previous test.

Don't overdo it. Simplify3D warns that plastic that's too cool stays partly solid and struggles to extrude, so you'd simply trade strings for under-extrusion. Stay within the range printed on the filament label and start from the manufacturer's slicer profile rather than a generic number. Our guide to print temperatures explains how to read those ranges.

Change one thing at a time. If you lower the temperature and lengthen retraction in the same run, you won't know which one fixed the problem, or which one caused a new one. Log every test along with the spool you used, since two filaments of the same material can behave quite differently.

Travel: speed, paths and print order

The time the nozzle spends over open air decides how much plastic can escape. Simplify3D suggests raising X/Y travel speed if your printer can handle it: less time in the air means fewer hairs. Go easy on a machine that already shakes, since aggressive moves can introduce other artifacts.

The path matters as much as the speed. Simplify3D offers an option to avoid crossing the outline during travel, and PrusaSlicer has an equivalent avoid crossing perimeters setting, so the nozzle stays over solid plastic instead of crossing open space. PrusaSlicer can also retract only when crossing perimeters. Any oozing that happens then stays hidden inside the walls.

Z-hop, which lifts the nozzle during travel, plays a role as well. Prusa notes that a lower lift improves stringing, while warning that turning it off entirely may let the nozzle hit the part. Finally, sequential printing, one object at a time, gives strings fewer chances to form between parts. The tradeoff is that you need to heed the collision warnings PrusaSlicer raises and keep a close eye on the print.

When strings survive every setting

If nothing changes, suspect the filament. Prusa recommends trying a different spool, because filament that has picked up moisture causes a lot of stringing. Drying the spool or opening a fresh one usually settles the question, and our filament dryer guide covers your options. Flexible filaments are a special case: they stretch as they retract, so they typically need longer retractions and plenty of tuning.

Next, check the nozzle. After long runs of a single material such as PETG, Prusa says a thin layer can build up in the nozzle and make strands stick to the print, so clean it thoroughly before printing. If the oozing seems to come from inside the hotend, Prusa points to a heat dissipation issue, fixed by reapplying thermal paste on the threads between the heatbreak and the heatsink. Parts that weren't reassembled correctly after a recent hotend swap can also be to blame.

For the last few hairs, Prusa mentions a quick pass with a heat gun set around 200 °C for one or two seconds. Holding it there longer can deform the part.

Sources and limits

• Simplify3D — Stringing or Oozing (print quality guide)
• Prusa Knowledge Base — Stringing and oozing

We organize manufacturer and community documentation; we have not measured these products ourselves. The manual for your exact model takes precedence over general guidance.