Wet Filament: How to Tell, and How to Dry It Properly

Most filaments absorb water from the air. Some take weeks to get bad and some take a day. When damp filament reaches the hot end, that water turns to steam inside the melt, and the steam is what ruins the print.

The signs

• Popping or hissing at the nozzle while it prints.
• Tiny bubbles or a rough, pitted surface on walls that should be smooth.
• Stringing that retraction tuning will not fix. Steam pushes plastic out of the nozzle during travel moves.
• Weak, brittle parts that snap along layer lines.
• Filament that snaps on the spool (common with damp PLA).

A quick test: print a small part, then dry the same spool and print it again. If the second print is clearly better, moisture was the problem.

How much each material cares

• Nylon absorbs water fastest. It can be noticeably wet within a day in a humid room.
• TPU and PETG get wet within days to weeks and print badly when they do.
• PC, ABS and ASA absorb moisture more slowly, but still print better dry.
• PLA is the most forgiving, but an old spool left out for months will still string and snap.

Filled filaments (carbon fibre, glass fibre) behave like the plastic underneath.

Drying temperatures and times

These are common starting points. Always check the spool label or the manufacturer's page first; brands differ.

• PLA: 45–50 °C for 4–6 hours. Do not go hotter: PLA softens at around 55–60 °C and the spool can fuse into a solid lump.
• PETG: 60–65 °C for 4–6 hours.
• TPU: 45–55 °C for 4–8 hours.
• ABS and ASA: 70–80 °C for about 4 hours.
• Nylon: 70–80 °C for 8–12 hours, then print straight from the dryer.
• PC: 70–80 °C for 6–8 hours.

The spool matters too. Some plastic spools soften at the higher temperatures, so check that the spool can take the heat, or rewind onto one that can.

What to dry it in

• A filament dryer is the easiest option. Most hold a set temperature, and many let you print straight from the box.
• A food dehydrator works well if it reaches the temperature you need. Check it with a separate thermometer; many run hotter or cooler than their dial says.
• Your printer's bed, with the spool covered by a box, works in a pinch, and some printers have a drying mode built in.
• A kitchen oven is the riskiest choice. Many ovens overshoot at low settings, and a few degrees too hot will ruin a spool of PLA. If you use one, check it with a thermometer first and never leave it unattended.

To check that drying worked, weigh the spool before and after. The weight it loses is the water that came out.

Keep it dry afterwards

Drying only helps if the spool stays dry. Store spools in an airtight box or bag with a few packets of silica gel and a cheap humidity card or hygrometer. Aim to keep the humidity inside under about 20 %. When the silica gel changes colour, dry it out and reuse it.

For nylon and TPU, print from a dry box or dryer so the filament never sits in room air during a long print.

Our filament database lists typical printing temperatures and properties for each material, so you can plan prints and drying together.