Filament dryer: why damp filament spoils a print

Why filament gets damp

Most plastics are hygroscopic, meaning they absorb water vapour from the air. PLA and PETG do so slowly, but after weeks in open air it shows. We write more about moisture under filament moisture.

When damp plastic reaches the hot nozzle, the water turns to steam and starts to spit. The result is bubbles, crackling, a matt surface, strings and, with longer exposure, lower strength.

How drying goes

A dryer is in principle a closed box with a heater and a fan. The spool is dried at a temperature below the point where it would start to deform. For PLA that is typically around 45 to 50 °C, for PETG around 60 to 65 °C, but the exact value is set by the filament maker.

It takes several hours. After drying, the spool is stored in an airtight container with silica gel, or the filament is fed from the dryer straight into the printer so that it does not get damp again.

When drying, make sure the temperature does not go above the point where the plastic starts to soften, see glass transition. A PLA spool can deform when overheated and then no longer unwinds properly.

It can be handled without a dryer too

With PLA and PETG it is often enough to keep spools in a closed bag with silica gel. A new spool from the maker usually comes in a vacuum bag. A dryer pays off if plastic sits for a long time in the open air, or with demanding materials such as nylon. We do not print those.

For your order

We look after the condition of the filament, and you do not have to do anything. We photograph every batch before dispatch. If a part arrives with a rough surface or is brittle, get in touch and we will look into it.