One of the most frustrating 3D printing problems to diagnose is wet filament. The symptoms look like a dozen different things - stringing, poor surface quality, blobs, brittle prints, crackling sounds - and people often spend hours tweaking slicer settings trying to fix something that is actually a materials storage problem.
This guide covers how to identify wet filament, how to dry it out, and how to store it so it does not happen again.
Most 3D printing filaments are hygroscopic - they absorb moisture from the air over time. When that moisture gets into the filament and you heat it to printing temperature, the water turns to steam inside the nozzle. That steam creates tiny bubbles and pressure spikes in the melt zone, which causes a range of visible problems.
It is not a sign that your filament is ruined. In most cases, drying the filament properly will restore it to its original quality.
Sounds:
Visual signs while printing:
Signs in the finished print:
If you hear crackling while printing, stop and dry your filament before continuing. Wet filament can also contribute to partial clogs over time, as moisture-affected material burns inside the nozzle.
Not all filaments absorb moisture at the same rate:
Very sensitive (dry before every print, store carefully):
Moderately sensitive (store with desiccant, dry if stored open):
Least sensitive:
A dedicated filament dryer (like the Sunlu S1 Plus or similar) is the easiest and safest method. You put the spool in, set the temperature, set a timer, and it handles the rest. Most can also dry filament while you print from it, which helps with long prints on sensitive materials.
See the best filament dryers guide for a comparison of the most popular options.
A food dehydrator works well and is often cheaper than a dedicated filament dryer. Make sure it fits your spool and can reach the right temperature.
Drying temperatures by material:
Do not exceed these temperatures. PLA will deform if dried too hot, and many spools use plastic that softens around 70-80C.
A kitchen oven works but requires care. Most ovens are not accurate at low temperatures - the actual temperature can be 20-30C higher or lower than the dial setting. Use an oven thermometer to verify the actual temperature before putting filament in.
Set the oven to its lowest setting and use a thermometer to measure the actual temperature inside. For PLA especially, exceeding 60C for long periods can cause the spool to warp or the filament to fuse together on the spool.
Leave the oven door slightly ajar to allow moisture to escape.
This will not dry filament quickly, but placing a wet spool in an airtight box with plenty of fresh silica gel desiccant will slowly pull moisture out over several days. It is the lowest-effort method but the slowest.
The how to store filament properly guide covers storage options and containers in more detail.