How to Dry Filament (and When You Actually Need To)

Most filament absorbs moisture from the air. When wet plastic reaches a hot nozzle, the water flashes to steam, and you see the result in the print. UK humidity makes this a real issue for a spool left out for a few weeks, so it is worth knowing how to check and fix it.

Signs your filament is wet

• Crackling, popping or hissing at the nozzle.
• Fine strings and blobs that do not go away with retraction tuning (see stringing).
• A rough, fuzzy or bubbly surface and weak layer bonding.
• Filament that snaps easily when you bend it, especially nylon and PLA that has been stored badly.
• Steam or tiny bubbles visible at the nozzle tip as it extrudes.

None of these is proof on its own, but together they point at moisture. Rule it out before adjusting temperatures or retraction.

Three ways to dry it

1. A filament dryer. A heated, enclosed box with a thermostat and timer, many of which let you print straight from the box. It is the most predictable method.
2. A food dehydrator. Often cheaper and big enough for a couple of spools. Use one with a thermostat that actually holds a low temperature.
3. A kitchen oven. We do not recommend it. Many ovens are poor at holding low temperatures and can overshoot, which warps spools and softens plastic.

Typical drying temperatures

These are approximate; the manufacturer’s guidance on the spool or box comes first.

Do not exceed the temperature your spool and the plastic itself can tolerate. PLA especially softens at modest temperatures, so err low and go longer.

Keep it dry afterwards

Drying is wasted if the spool goes back into a damp room. Store spools in an airtight box or a vacuum bag with fresh desiccant, and add a small hygrometer to see the humidity inside. Many people aim for relative humidity below roughly 20% for the more sensitive materials. Print straight from a dry box for nylon and PVA-type supports.