Do you need to dry PLA and PETG? Why it matters and how to do it

The short answer

PETG is the one to take seriously. PLA is more forgiving, but it can still cause trouble once a spool has been open for a while or the room is damp. Both plastics pick up water from the air. When that water reaches a hot nozzle it turns to steam, and the plastic comes out foamy and inconsistent. Bambu Lab's drying guide lists the results: stringing, oozing, small holes, rough surfaces and weaker parts. It also says the problems get worse as room humidity rises and the longer a spool sits exposed.

Drying is not something you have to do before every print. Prusa's knowledge base treats it as a fix for symptoms, and it lists nylon, PVA and flexible TPU as the materials that need it far more often than PLA. Owners on the Bambu Lab community forum mostly say the same about PLA. In a thread asking whether an eight-hour PLA cycle is really needed, most replies said they only dry when they see brittleness, popping or stringing. They also said climate matters more than any fixed rule.

What happened on my 16-hour PETG print

Here is my own example. I've had a Bambu Lab P2S Combo for about a month and roughly 25 prints. The AMS 2 Pro sits on top of the printer, and I bought the setup at Best Buy Canada. Most of my printing has been Bambu PLA and wood-fill PLA, plus some Bambu PETG. The longest job so far was a white PETG decorative mask that took about 16 hours. I printed it from a spool I had not dried.

The mask came out well overall, but thin hair-like strings crossed the eye and mouth openings. They pulled away by hand, so nothing was ruined. Still, it is the kind of defect that drying is meant to prevent. I haven't reprinted the mask with dried filament yet, so I can't show you a before-and-after. It does match what manufacturers and other owners describe for PETG. My full impressions of the printer are in the hands-on review at Bambu Lab P2S Combo (AMS 2 Pro) review.

Signs a spool needs drying

You can't see moisture in filament, so look for these symptoms instead:

Popping or crackling at the nozzle, sometimes with small puffs of steam. Forum owners describe this sound most often with wet PETG.

Stringing or fuzz that the same spool didn't produce when it was new. Prusa notes that some filaments string by nature, so compare a spool against its own earlier prints rather than against a different brand.

Rough, bubbly or dull surfaces, blobs, or weak layers. Prusa lists all of these.

Brittle PLA that snaps in the feed path. Forum owners mention this most often with spools that have been open for months.

There is good evidence behind this for PETG. In a 2025 study in the journal BioResources, researchers exposed two rolls of PETG to humid air. They dried one roll at 70 °C for a total of 8 hours and left the other wet. Parts printed from the dried roll had smoother surfaces and higher tensile strength. CNC Kitchen, the testing channel run by Stefan Hermann, reported something similar in a write-up on a desiccant cabinet. Among the spools he had left out in the open, PETG showed the clearest print-quality difference.

Recommended temperatures and times

Stay below the temperature where the filament softens. Otherwise the coils can fuse together or the spool can warp. These are the figures the manufacturers publish:

Bambu Lab, for its own PLA Basic and PLA Matte: 50 °C for 8 hours in a forced-air oven, 45 °C for 12 hours in the AMS 2 Pro, or 60 to 70 °C for 12 hours on the heated bed of an enclosed printer. If you use the bed, cover the spool and flip it every 6 hours. Bambu marks drying as required for its PLA Wood and suggests 55 to 65 °C for 8 hours in an oven.

Bambu Lab, for PETG and PETG-CF: 60 to 65 °C for 8 hours in an oven, 65 °C for 12 hours in the AMS 2 Pro, or 75 to 85 °C for 12 hours on the bed.

Prusa, for Prusament: PLA at 45 °C for 6 hours and PETG at 55 °C for 6 hours. Prusa warns that going hotter can soften the filament until it sticks to itself.

Polymaker: PolyLite PLA at 55 °C for 6 hours and PolyLite PETG at 60 °C for 6 hours. It notes that both are only needed if the material has absorbed moisture. For PETG that has been exposed a long time in hot, humid conditions, Polymaker says to run a longer cycle.

The numbers vary because each company makes its plastic differently. If your spool's label or data sheet gives a figure, use that one. If not, start at the lower end of the ranges above.

Four ways to dry, from best to riskiest

A dedicated filament dryer or a drying AMS is the simplest option. You set a temperature and a timer and walk away. If you own an AMS 2 Pro, Bambu's RFID tags load the settings automatically for its own filaments. I explain how that works, including the limits, in a separate guide on drying with the AMS 2 Pro.

A food dehydrator is a popular cheap alternative. CNC Kitchen tested one and found that weight loss mostly stopped after about 12 hours. Stefan Hermann wrote that 4 to 6 hours was often enough for PLA and PETG. He also measured an uneven temperature from the top tray to the bottom, so check yours with a thermometer.

Your printer's heated bed works if the printer is enclosed. Bambu's wiki covers this for its enclosed models, including the P2S. Unload the filament from the toolhead first, put a cover or the cardboard box over the spool, close the door and flip the spool halfway through. Bambu says open-frame printers such as the A1 can't dry filament this way.

A kitchen oven is the last resort. Bambu tells people not to use one at all. Prusa explains that home ovens measure temperature poorly, often can't go low enough, and can overshoot enough to damage the filament. If you have no other option, check the oven with a separate thermometer and keep the spool well away from the heating elements.

Keep it dry afterwards

Drying only helps if the spool stays dry. Bambu's guide says that at a typical indoor humidity of about 55% RH, freshly dried filament can pick up enough moisture to affect prints within 2 to 12 hours, depending on the material. Below 20% RH, Bambu says it generally stays dry for 2 to 7 days. Seal the spool in a container with fresh desiccant as soon as the cycle finishes, or move it straight into a closed AMS.

CNC Kitchen's testing suggests storage can even finish part of the drying. He found that a sealed box with plenty of silica pulled a significant amount of moisture out of PLA and PETG over a week. His desiccant cabinet removed most of the moisture he could take out of PLA and PETG without heat. Nylon was the exception and still needed a heated dryer. If you print PLA most of the time, good storage may be all you need. I cover that in a separate guide to storing filament in a Canadian home.

When drying isn't the answer

Some stringing has nothing to do with moisture. On the Bambu forum, one PETG owner found that stringing got worse after a second drying cycle because the settings had been tuned while the filament was still damp. Another owner dried translucent PETG for 12 hours and saw no change. In that case, turning off scarf seams and reducing cooling fixed the problem. One owner who has printed with PETG for years, in a basement averaging about 78% RH, argued that drying only adds the last bit of polish for him. Other replies in that thread strongly disagreed.

Two things explain the disagreement. Brands absorb water at different rates, and climates vary a lot. Treat drying as the first thing to rule out, not as a guaranteed fix. If a dried spool still strings, the next step is temperature and retraction tuning, which my PETG stringing guide covers.

From a tech standpoint

Dry PETG before long or visible prints, using the manufacturer's temperature rather than the hottest setting you can find. Dry PLA when it shows symptoms, and always dry speciality types such as wood-fill. Weighing a spool before and after drying is a cheap way to confirm the cycle actually removed water. Then seal the spool with desiccant right away, or the effort is gone within hours.