How to fix PETG stringing: causes and fixes that actually work

Why PETG strings more than PLA

PETG is tough and handles heat better than PLA, but it has a reputation for leaving thin strands between parts of a print. Prusa's knowledge base lists stringing as one of PETG's main drawbacks, along with poor fine detail and a tendency to bond very strongly to smooth print surfaces. In practice, the plastic stays runny and sticky in the nozzle. When the nozzle travels across an open gap, a little material oozes out and pulls into a hair-thin thread.

A small amount of wispy stringing is normal for PETG. Heavy cobwebs, blobs or a rough, bubbly surface mean something is wrong, and the most common cause is moisture in the filament.

My own example: a 16-hour mask with strings across the openings

I ran into this myself on the Bambu Lab P2S Combo I bought at Best Buy Canada. I've had it about a month and printed roughly 25 jobs, mostly Bambu PLA and wood-fill PLA, with some Bambu PETG. My longest print was a white PETG decorative mask that took about 16 hours. I didn't dry the spool first. The ridges and recesses came out cleanly, but fine strings ran across the eye and mouth openings. Those openings are exactly where the nozzle has to travel over empty space.

The strings pulled off by hand and left the surface intact. I haven't reprinted the mask with dried filament yet, so I can't say how much of the stringing drying would remove. Skipping the dryer was still the obvious first thing to rule out. My full notes on the printer are in the hands-on review at Bambu Lab P2S Combo (AMS 2 Pro) review.

Step 1: Rule out moisture

The manufacturer guidance behind this article consistently puts drying first. Polymaker's PETG instructions say plainly that if stringing occurs, dry the filament before changing anything else. Bambu Lab's drying guide explains the cause. Absorbed water turns to steam in the hot nozzle, the melt expands and comes out erratically, and you get stringing, oozing and rough surfaces. Polymaker also describes its PETG as very hygroscopic, meaning it absorbs water readily.

Use the filament maker's drying figures. Bambu lists 60 to 65 °C for 8 hours in a forced-air oven for its PETG, or 65 °C for 12 hours in the AMS 2 Pro. Polymaker suggests 60 °C for 6 hours for PolyLite PETG. Prusa recommends a gentler 55 °C for 6 hours for Prusament PETG.

Signs that moisture is to blame include popping or hissing at the nozzle, a spool that printed cleanly when it was new, and stringing that doesn't change when you lower the temperature. CNC Kitchen's Stefan Hermann adds a less obvious effect. He explains that water at printing temperature breaks down the polymer chains, which lowers the melt's viscosity and leads to even more stringing. In his desiccant-cabinet write-up, PETG showed less stringing and foaming after storage in dry air.

Step 2: Confirm the spool is actually dry

Owners on the Bambu Lab community forum offer a useful warning here. A dryer's humidity reading tells you about the air inside the dryer, not the plastic. The practical test they suggest is to weigh the spool before and after drying. When the weight stops dropping, the spool is as dry as that method will get it.

Re-absorption is the other trap. Bambu's guide says freshly dried filament in a room around 55% RH can take on enough moisture to affect prints within 2 to 12 hours. Dry the spool, then print it from a sealed AMS or dry box rather than leaving it on an open spool holder overnight.

Step 3: Lower the nozzle temperature in small steps

If a dry spool still strings, temperature is the next thing to adjust. Teaching Tech's calibration site, which accompanies the YouTube channel, explains that hotter nozzles ooze more and cooler ones ooze less. Prusa recommends a lower nozzle temperature combined with more retraction for PETG.

Stay inside the manufacturer's range. Bambu lists 240 to 270 °C for standard PETG and 230 to 260 °C for PETG HF and translucent PETG. Polymaker gives 240 to 260 °C for PolyLite PETG. One forum example shows how much this can matter. An A1 owner fighting heavy stringing with a third-party high-speed PETG got much better results by dropping to 240 °C and keeping the first layer at 250 °C. Go down 5 °C at a time and check layer bonding as you go, because PETG that runs too cool loses the toughness you chose it for.

A temperature tower speeds this up. Teaching Tech's site generates one and points out that temperature and retraction affect each other, so you may need to go back and forth between them.

Step 4: Tune retraction, but only a little

Retraction pulls the filament back before a travel move so less plastic oozes out. Teaching Tech's method is to print a retraction tower, change only one setting per test, and start with retraction distance because it matters most. Polymaker's published starting points for PolyLite PETG are 1 mm at 20 mm/s on a direct-drive extruder. On a Bowden setup, it suggests 3 mm at 40 mm/s.

Owner reports on the Bambu forum are mixed here. Some fixed stringing with a small retraction change, while others found that more retraction made no difference or made things worse. That's a good reason to move in small steps rather than doubling the value.

Step 5: Check seams, cooling, travel and the nozzle

Several of the most effective fixes owners report are not stringing settings at all.

Scarf seams: A P1S owner printing Bambu's translucent PETG dried the spool for 12 hours with no improvement. Turning off the scarf joint seam setting removed almost all of the stringing.

Nozzle buildup: The same owner cleaned PETG residue off the nozzle with a brass brush, calibrated the filament and reduced cooling. After that, both stringing and blobs nearly disappeared. A Bambu forum reply also points out that some PETG residue on the nozzle is normal.

Speed: Slowing down can backfire. Forum owners note that a slower nozzle gives the plastic more time to ooze during travel. Another owner found that very low acceleration made travel moves sluggish and added strings.

Cooling: Prusa suggests printing the first layers with the fan off and then running it at about half power for a balance of detail and strength. Polymaker's recommended fan range for its PETG is 20 to 60%.

Leftover strings: If you only have a few thin strands, as on my mask, they may simply pull off by hand. Treat that as cleanup, not a fix. The causes above are still worth working through before your next long print.

From a tech standpoint

Dry the spool and confirm it by weight first, because no amount of retraction tuning will make up for wet PETG. If strings remain, lower the nozzle temperature 5 °C at a time within the maker's range. After that, adjust retraction in small steps, then look at seams, cooling and nozzle cleanliness. Change one setting per test print, or you won't know which change actually fixed it.