3D printer stringing: what causes those wispy threads and how to fix it

Stringing happens when molten filament keeps oozing out of the nozzle while the printhead is travelling between features. The plastic is hot enough to stretch but cool enough to leave a wispy trail behind. You end up with a print covered in fine hairs, or little blobs hanging off the side of towers and lettering.

It is one of the most common things people ask us about, and ninety percent of the time it is fixable from the slicer. The other ten percent is the printer or the filament itself.

What stringing actually is

When the nozzle finishes one island of plastic and moves across an empty gap to start the next, you do not want any filament coming out during that travel. The slicer tries to stop the ooze by pulling the filament back a few millimetres before the move. That pull-back is called retraction.

If retraction is too short, too slow, or the plastic inside the nozzle is too runny, some of it dribbles out anyway. The nozzle drags that dribble across the air gap, and it cools mid-flight into a thin string. Multiply that by hundreds of travel moves and you get a print that looks like it has been wrapped in cobwebs.

Stringing is almost always cosmetic. It does not weaken the part. But it ruins the finish on anything with detail, and on PETG it can build up into blobs that knock the nozzle off course on later layers.

Why your printer is stringing

There are really only four causes worth chasing, in this order.

Wet filament. This is the number one cause and people ignore it constantly. Filament absorbs water from the air. When it hits the hot nozzle, that water flashes to steam and blows little bursts of plastic out during travel moves. PETG, nylon and TPU drink water fast. PLA is slower but not immune. If a fresh spool prints clean and a six-month-old spool from the same brand strings everywhere, the filament is wet. Dry it.

Nozzle too hot. Every filament has a window. PLA usually wants 195 to 215 deg C. PETG sits around 230 to 245. If you are at the top of the range, the plastic is thinner and oozes more freely. Drop the temperature in 5 degree steps and reprint a stringing test until it cleans up or the layers stop bonding.

Retraction too weak. On a direct-drive printer (the extruder sits on the printhead) you usually want 0.5 to 1.5 mm of retraction. On a Bowden setup (the extruder is bolted to the frame and pushes filament down a tube) you need much more, typically 4 to 7 mm, because the tube has slack in it. Retraction speed of 35 to 45 mm/s is a sensible starting point.

Worn or wrong nozzle. A brass nozzle that has run a few kilos of filament gets sloppy at the tip. The opening is no longer a clean circle, so flow control gets worse. If the printer used to print clean and has slowly got stringier over months, swap the nozzle for a fresh one before you blame the slicer.

How to dial it out yourself

This is genuinely a DIY job for most people. You do not need to send a printer in to fix stringing. Work through it in this order.

1. Dry the filament. Put the spool in a filament dryer or a food dehydrator at the temperature your filament's data sheet recommends, usually 45 to 55 deg C for PLA and 65 to 70 deg C for PETG, for four to six hours. If you have no dryer, an oven set to its lowest setting with the door cracked open works in a pinch, but watch it. 2. Print a stringing test. Search for a temperature tower or a stringing test on Printables. They print fast and give you a clear visual answer. 3. Drop nozzle temperature 5 deg C and reprint. Keep going until either the stringing clears or you start losing layer adhesion. Back off one step from there. 4. If stringing is still there, raise retraction distance by 1 mm at a time. On Bowden go in 2 mm steps. Do not push past 8 mm on direct-drive or you will start grinding the filament. 5. If you are still stringing, look at travel speed. Faster travel gives the ooze less time to form a string. Try 150 to 200 mm/s on travel moves if your printer can handle it without ringing. 6. Turn on combing or avoid-crossing-perimeters in your slicer. That keeps the nozzle inside the part during travels, so any tiny ooze ends up hidden inside the walls.

Do not change more than one variable at a time. That is the rule everyone breaks and then cannot work out what fixed it.

PETG is its own thing

If you only ever printed PLA and have just switched to PETG, expect stringing for the first few prints. PETG is sticky and stays molten longer than PLA. The settings that gave you a glassy PLA print will absolutely string on PETG.

For PETG, we usually start at 235 deg C, retraction 4 mm on Bowden or 1 mm on direct-drive, retraction speed 25 to 30 mm/s, and a travel speed of 150 mm/s. Drying the spool first is not optional with PETG. It is the single biggest variable.

DIY or send it in

DIY this one. Stringing is a settings and filament problem, not a hardware fault, in the vast majority of cases. There is no point paying anyone to adjust slicer settings you can adjust yourself in ten minutes.

The exception is when stringing came on suddenly and other symptoms came with it. If the print is also under-extruding, clicking, or the nozzle is leaving inconsistent line widths, the issue is upstream of the slicer. That could be a partially clogged nozzle, a failing heatbreak, a worn PTFE liner, a tired hotend thermistor reading the wrong temperature, or an extruder gear chewing the filament. Those are repair jobs.

Stringing vs blobbing vs zits

People use these words interchangeably and they are not the same thing. Stringing is the wispy hair between features. Blobs are little raised lumps at the start or end of a perimeter, caused by pressure in the nozzle not being released cleanly. Zits or pimples are tiny bumps on the surface from coasting and seam settings. They overlap, but the fixes are different. If your print has hairs in the air gaps, you have stringing. If your towers have a vertical seam of dots running up one side, that is a seam issue, not stringing.

When to mail it in

If you have dried the filament, walked through the temperature and retraction steps, and the printer is still leaving strings or blobs, the problem is probably mechanical. A clogged or worn hotend, a slipping extruder, or a thermistor that is reading 10 degrees off will all look like stringing from the outside. We can diagnose and repair the hotend, extruder, mainboard or thermistor on most Creality, Bambu, Prusa and Anycubic machines as a mail-in job, usually within a few working days once it lands on the bench. Get in touch through /contact.html with a photo of a failed print and the brand and model, and we will tell you whether it is worth sending in or a part order will fix it at your end.