Filament moisture: why damp filament is a problem

Why filament absorbs water

Most plastics are hygroscopic, so they slowly draw moisture from the surrounding air. PLA and PETG absorb relatively slowly, but a few weeks in the air is enough. With nylon and TPU it is even faster. A box with silica gel, which is a desiccant, slows the moisture down, but it will not dry a spool that has already got wet.

How to tell

Damp filament spits and crackles in the nozzle, forms tiny bubbles and pimples on the surface and leaves strings behind (stringing). The surface is matte and rough, the part can be brittle and the layers hold less well. With PETG the stringing is often pronounced. The sure protection is correct storage in sealed bags and a filament dryer.

How filament is dried

A dryer or an oven at a low temperature for several hours. Usually around 45 to 55 °C for PLA and around 60 to 65 °C for PETG, always below the softening temperature. At home, better check the temperature and time with the spool manufacturer. A home oven is often inaccurate, and at a higher temperature the spool deforms.

What this means for you

You do not need to do anything for an order, as you do not supply the filament. We photograph every batch before it ships. We do not sell filament. If you print at home, dry PETG in particular before printing and do not leave spools uncovered in a damp room.

How moisture affects a part

Damp filament is not just a cosmetic problem. The steam in the nozzle creates tiny cavities inside the wall, which weaken the part. With PETG this shows as a matte surface and a weaker bond between layers. With PLA the parts tend to be brittle and snap at a thin point.

The most common mistake is a spool forgotten in the printer for weeks. A sealed box with silica gel helps, or a dryer you can also print from directly. Once a spool goes back in its bag, it lasts much longer.