Stringing in 3D printing — 6 causes and how to fix it

Symptom: after printing, the model is covered in thin, cobweb-like strands of plastic — most often between separate towers, inside holes and over open spaces. The surface itself is fine, but the print looks as if it has been wrapped in a net.

Stringing (also called hairing) happens when molten plastic leaks out of the nozzle while the head travels across an open space. The nozzle is not printing, but the material is still under pressure and flows out on its own. It is one of the most common problems with PETG and TPU, and with PLA it usually means the temperature is too high or the filament is wet.

The most common causes and their fixes

1. Retraction is switched off or too short

Retraction pulls the filament back before a travel move to take the pressure off the nozzle. If it is switched off or the distance is too small, plastic leaks out on every travel move.

What to do: in the slicer, find Retraction distance. For a direct drive extruder start at 0.5–1.5 mm. For a Bowden extruder, at 3–6 mm. Increase in steps of 0.5 mm and print a test every time — do not change two parameters at once.

Note: too much retraction causes the opposite problem — holes at the start of a line and the drive wheel grinding the filament.

2. The nozzle temperature is too high

The hotter the plastic, the thinner it is — and the more easily it flows out by itself. This is the most common cause of stringing with PLA.

What to do: lower the temperature by 5 °C at a time and print a temperature tower. Go down to the bottom of the range for the material — below that you will get poor layer bonding.

Porima material	Nozzle range	Tendency to string
PLA	200–230 °C	Low
Tough PLA (PLA+)	210–240 °C	Low
Hyper PLA+	220–250 °C	Low
PETG	240–260 °C	High
PETG Transparent	240–260 °C	High
HT PETG	270–300 °C	Medium
ABS	250–280 °C	Medium
ASA	250–280 °C	Medium
TPU Flex 98A	230–260 °C	High
PA (nylon)	260–290 °C	Low

Source: the official FDM technical data table from the manufacturer, Porima. The full set: print temperature table.

3. The filament has absorbed moisture

This is the cause people overlook most often. Water in the filament boils off inside the nozzle and tears the stream of plastic apart — the result is strands, bubbles and the characteristic crackling during printing. PETG, TPU and nylon absorb moisture within a few days of the packet being opened.

How to check: listen to the nozzle. Crackling and hissing mean moisture. The second sign is a dull, rough surface where the material should be smooth.

What to do: dry the spool before printing.

Material	Drying temperature	Time
PLA and PLA variants	30–40 °C	2–4 h
PETG	30–40 °C	2–4 h
HT PETG	50–60 °C	6–12 h
ABS / ASA	40–60 °C	6–12 h
TPU Flex 98A	40–60 °C	2–4 h
PA (nylon)	65–80 °C	8–12 h — mandatory
PLA/CF	55 °C	4 h
HIPS	Not needed — the material is not hygroscopic

Full guide: drying filament — temperature and time for every material.

4. The travel speed is too low

The longer the nozzle hangs over an open space, the more material has time to leak out. A faster travel move shortens that time.

What to do: raise Travel speed to 150–200 mm/s, as far as the printer's mechanics will stand it. If vibration and ghosting appear, come back down by 25 mm/s.

5. "Combing" / "Avoid crossing perimeters" is switched off

This function routes the head inside the already printed area instead of over empty space. Fewer travel moves over thin air means fewer strands.

What to do: in PrusaSlicer and OrcaSlicer turn on Avoid crossing perimeters. In Cura set Combing Mode to Not in Skin.

6. A worn or dirty nozzle

Plastic residue on the outer edge of the nozzle collects the leaking material and smears it across the model. A worn nozzle does not cut the stream off cleanly.

What to do: clean the nozzle hot with a brass brush. If you print with abrasive materials — PLA/CF requires a hardened nozzle and eats brass within a few dozen hours — change the nozzle for a steel or carbide one.

When it is not the settings

If stringing appears suddenly on a material that used to print cleanly, suspect moisture or a change of filament batch first. An unstable diameter causes swings in nozzle pressure that no retraction setting will compensate for. Porima filaments are produced to a ±0.03 mm tolerance.

Related problems

• Wet filament — crackling in the nozzle, a dull surface, bubbles. The most common hidden cause of stringing.
• Blobs & zits (lumps on the surface) — the same nozzle pressure mechanism, a different symptom.
• Filament grinding — appears when retraction is set too aggressively.
• Clogged nozzle — a partial blockage gives uneven flow that gets mistaken for stringing.
• Scorching and discolouration — also a result of too high a temperature.
• Under-extrusion — the opposite problem, usually after dropping the temperature too far.