Stringing and Oozing: Why It Happens and How to Fix It
2026-08-22
Where the strings come from
When the print head travels from one part of a model to another, molten plastic keeps seeping out of the nozzle. A fine thread trails behind it and sets as a bridge between the parts: the model ends up covered in cobwebs, and the walls collect blobs and smears. It does not ruin the whole part - the hairs come off - but the surface is never quite the same after cleanup, and on fine geometry the strings glue elements together.
The fix works from two sides: remove the cause of the excess flow, and set up retraction - pulling the filament back before a travel move.
Cause number one: wet filament
Before touching slicer settings, check the spool. 3D printing plastic is hygroscopic: water absorbed from the air boils inside the nozzle, makes the melt runnier and pushes it out even where extrusion has stopped. Wet filament strings far worse than dry, and no retraction setting can compensate for that.
The signs: crackling or hissing in the nozzle, a cloudy rough surface, and a sudden jump in stringing on a spool that used to print clean. The details are in how to dry filament. In short: PETG dries for 6-8 hours at 60-65 °C, TPU for 6-8 hours at 50-55 °C, and afterwards the spool lives in a bag with silica gel.
Retraction: how far to pull back
Retraction distance depends on the drive type, not on the idea that more is better:
- Direct drive (the extruder sits on the head): the pull is short. For TPU it is 0.5-1.5 mm, and that minimum is deliberate: on a long pull the soft filament buckles and jams inside the extruder.
- Bowden (the extruder sits on the frame, a tube runs to the head): the filament springs inside the tube, so the pull has to be longer. For PETG on a Bowden setup the working range is 4-6 mm.
Too much retraction does not print cleaner - it prints worse: the melt gets dragged up the hot zone and the risk of a clog appears. Increase it gradually and check every change with the test below.
Temperature: the hotter, the runnier
Overheated plastic flows out of the nozzle on its own. If stringing appeared together with a temperature increase, come back to the lower part of the material's range: 220-250 °C for PETG, 220-240 °C for TPU, 190-220 °C for PLA. Start at the bottom of the range and raise it only when the layers bond poorly.
Travel speed
The faster the nozzle moves between parts of the model, the less time the melt has to escape and stretch into a thread. Raise the travel speed in the slicer and enable combing (avoid crossing perimeters) - the nozzle then spends less time over open surfaces.
How to test: two towers
The standard test is two thin towers printed a distance apart: the nozzle travels between them on every layer, so strings show up immediately. Print the test, change one setting, print again. Changing two settings at once only gets in the way - you will not know which one worked.
The material matters
PETG strings more readily than PLA by nature - that is a property of the material, not a printer defect. TPU, with its minimal retraction, almost always leaves a few hairs, and they come off a finished part easily. The helper can pick a material for you, and the full printing parameters live on the PETG and TPU pages.
Frequently asked
- Why does my 3D print have strings between parts?
- During travel moves the melt seeps out of the nozzle and stretches into a thread. The most common cause is wet filament, followed by too little or disabled retraction and a nozzle temperature set too high.
- What retraction should I use for PETG?
- On a Bowden setup the working range is 4-6 mm; direct drive needs noticeably less. If strings remain, dry the spool first: wet PETG strings far worse than dry.
- Why does TPU string so much and what can I do?
- Soft filament cannot take a long retraction - it buckles and jams in the extruder. Set 0.5-1.5 mm, print on direct drive at 15-30 mm/s, and dry the spool for 6-8 hours at 50-55 °C.
- Does drying filament help against stringing?
- Often it is the main cause: water boils in the nozzle and pushes the melt out. If a spool used to print clean and then started stringing, dry it first and only then touch the slicer settings.