Why Does My Filament Need Drying?
PETG, nylon, TPU, and PC are hygroscopic — they pull moisture out of the air even sitting on an open spool holder, not just from a spilled drink. Printing wet filament causes stringing, popping/crackling sounds at the nozzle, and pitted or weakened layers, because trapped moisture flash-boils inside the melted plastic as it exits the nozzle. It's a print-quality problem, not a health hazard.
Drying temperatures and times by material
| Material | Dry temp | Dry time | Note |
|---|---|---|---|
| PLA | 40–45°C | 4–6 hrs | Lowest priority; humid climates benefit occasionally |
| PETG | 60–65°C | 6–8 hrs | Don't exceed ~70°C — nears PETG's glass transition |
| TPU | 50–60°C | 6–8 hrs | Lower than PETG — TPU deforms more easily while soft |
| PC | 70–80°C | 8–10 hrs | Skipping this commonly causes bubbling |
| Nylon (PA) | 75–90°C | 8–12 hrs | Most hygroscopic material here — absorbs within hours |
Aggregated from manufacturer drying guidance (Bambu Lab, Polymaker, Overture) — always check the specific spool's own instructions first. Full dataset: The 3D Printing Numbers.
Why moisture causes these specific defects
Water absorbed into the filament's polymer structure turns to steam the instant it hits nozzle temperature. That steam has to escape somewhere — through the melted plastic as it's being extruded — which shows up as tiny pops/cracks, stringing between features, and a rougher, sometimes foamy-looking surface. In nylon specifically, enough absorbed moisture can also weaken the printed part's mechanical strength, since the steam creates microscopic voids in each layer.
Keeping filament dry between prints
Drying fixes an already-wet spool, but it doesn't protect a spool left open afterward. Store hygroscopic filament sealed — a bag with the air pressed out plus a desiccant pack, or a gasketed storage bin — or use an active dry box that feeds filament through a sealed port while printing, so it never sits exposed between drying and use.
Frequently Asked Questions
Audible popping or crackling sounds at the nozzle during extrusion, visible stringing that wasn't there before, a rougher/bumpier surface finish, and small steam-like wisps near the nozzle are the common tells. If a spool has been open more than a couple of weeks in a normal-humidity room, assume it needs drying before a critical print.
Some people do, but a kitchen oven's temperature control is usually far less precise than a dedicated filament dryer or a food dehydrator, and overshooting a material's glass transition temperature can deform the spool. A dedicated dryer box with a real thermostat is the safer, repeatable option.
PLA is the least moisture-sensitive of the common materials and often prints fine for a long time without drying, but it is not immune — in humid climates or after months of open storage, even PLA can show minor stringing that clears up after a short dry.
That depends entirely on how it's stored afterward — a spool dried once and then left on an open holder in a humid room can start re-absorbing moisture within days. Sealing the spool in a bag or bin with desiccant, or using an active dry box with a sealed feed port, is what actually keeps it dry between prints.