How to Dry Filament — and Why Wet Filament Looks Like a Broken Printer
Moisture causes more "printer faults" than any hardware problem. How to spot it, how to dry each material, and how to stop it coming back.
Your printer was working fine last month. Now there is stringing everywhere, the surface is rough and blotchy, layers snap apart, and the nozzle is making a faint crackling sound. You have re-levelled, changed the nozzle and re-tuned retraction, and nothing helps.
It is almost certainly the filament.
Why filament gets wet
Most filaments are hygroscopic: they absorb moisture from the air. Some absorb it slowly, others very quickly. When the filament reaches the hot nozzle, that absorbed water turns to steam. The steam bubbles cause every symptom above, which is why wet filament so often looks like a hardware fault to someone who has not seen it before.
The symptoms
- Popping, crackling or hissing at the nozzle. This is the clearest sign.
- Stringing and blobs, even after retraction tuning.
- Rough, bubbly or matte patches on surfaces that should be smooth.
- Weak, brittle parts that snap along layer lines.
- Filament that breaks when you bend it (especially PLA).
How sensitive is each material?
PLA: mildly sensitive. It will usually print fine for weeks in the open, but an old spool in a humid room will start stringing and become brittle.
PETG: noticeably sensitive. Stringing is the first sign. Dry it if it has been out for more than a week or two.
TPU: very sensitive. Dry it before every serious print.
Nylon (PA) and PA-CF: extremely sensitive. A spool can absorb enough moisture to print badly within hours. Nylon should be dried before use and printed straight from a dry box.
PC, PVA and other soluble supports: very sensitive. PVA in particular can be ruined by a day of humid air.
How to dry it
A dedicated filament dryer is the easiest option: it heats the spool to a set temperature for a set time, and many let you print straight from the dryer. As a guide:
- PLA: 45–50 °C for 4–6 hours
- PETG: 60–65 °C for 4–6 hours
- ABS / ASA: 65–80 °C for 4 hours
- TPU: 50–55 °C for 4–8 hours
- Nylon: 70–80 °C for 8–12 hours
Always check your filament manufacturer's recommendation. Too much heat will fuse a spool into a solid block.
Other options: some multi-colour units dry filament while printing, including the Anycubic ACE Pro that comes with the Kobra 3 Combo and Kobra S1 Combo. The heated beds on some printers can dry a spool under a cover. A food dehydrator works well if it holds a steady temperature. Do not use a kitchen oven. Many cannot hold low temperatures accurately, and spools can melt or warp.
Keeping it dry
Drying fixes the problem; storage prevents it. Keep opened spools in an airtight box or a vacuum bag with silica gel desiccant, and a cheap humidity meter so you can see when the desiccant needs recharging. Aim for below 20 % relative humidity for nylon and TPU, and below 40 % for everything else.
Is a dryer worth buying?
If you print anything other than PLA, or you live somewhere humid, yes. It is among the cheapest upgrades in the hobby, and it will save you more wasted filament, failed prints and troubleshooting than almost anything else you can buy. It is the first accessory we recommend with any printer.