Every filament absorbs water from the air. What differs is how fast, and how much it ruins the print. PLA can sit open on a shelf for months and print fine. Nylon left out overnight will hiss in the hotend the next morning.
How to tell filament is wet
Three signs, in order of how obvious they are:
- Sound. Popping, crackling, or hissing at the nozzle. Water in the melt flashes to steam and escapes through the extrudate.
- Surface. Rough, fuzzy walls where they should be smooth, and stringing that no retraction setting fixes.
- Strength. Steam bubbles interrupt the bond between layers, so a wet part snaps at loads a dry one shrugs off.
If a spool used to print well and now does not, moisture is the first thing to check, ahead of any slicer setting.
Drying temperatures by material
Dry below the glass transition temperature or the spool fuses into a solid lump. These are the ranges the manufacturers publish:
| Material | Temperature | Time |
|---|---|---|
| PLA | 45 to 55 °C | 4 to 6 hours |
| PETG | 60 to 65 °C | 6 to 8 hours |
| ABS / ASA | 70 to 80 °C | 8 hours |
| TPU | 55 to 70 °C | 4 to 8 hours |
| Nylon (PA) | 80 °C | 12 hours |
Carbon and glass filled versions of any of these hold more water than the unfilled polymer, so use the longer time.
Dryer, oven, or heated bed
A filament dryer is the right tool. It holds a low temperature accurately and vents humid air, and you can print straight from it.
A kitchen oven works if it can hold a genuinely low temperature. Many cannot: an oven set to 50 °C often swings between 40 and 90 °C, and 90 °C turns a PLA spool into a frisbee. Test with an oven thermometer before you trust it with a spool.
A printer heatbed with a box over it is the improvised option. Bambu documents this for its own materials, using bed temperatures around 75 to 100 °C for twelve hours on materials that tolerate it. It is slow and imprecise but free.
Do not use a food dehydrator without checking its actual temperature, and never microwave filament.
Keeping filament dry afterwards
Drying is a fix. Storage is the prevention.
- Sealed bag plus fresh desiccant is enough for PLA, PETG, ABS, and ASA.
- Nylon, TPU, and anything fibre filled want a sealed dry box with a hygrometer, and ideally printing straight from that box.
- Silica gel that has changed colour is saturated and doing nothing. Regenerate it in the oven or replace it.
Aim for under 20% relative humidity inside the container. Above about 40% you are storing filament in a slow soak.
Which materials actually need this
Ranked by how much drying changes the outcome:
Always dry: nylon, TPU, carbon or glass filled anything, PVA and other water-soluble supports.
Dry when it has been open a while: PETG, ABS, ASA, PLA-CF.
Rarely needs it: plain PLA, unless you live somewhere humid or the spool has sat unbagged for months.
If you print mostly PLA, a dryer is a luxury. If you print nylon or TPU, it is part of the machine.
The five minute diagnosis
Print a 20 mm cube with the outer wall exposed. Listen while it runs and look at the finished walls. Quiet nozzle and smooth walls means the filament is fine and your problem is somewhere in the slicer. Popping and fuzz means stop tuning settings and start drying.