Storage and drying: why moisture matters so much

Most 3D printing filaments are hygroscopic: they slowly draw moisture out of the air. PLA and PETG are affected; some engineering materials, such as nylon (PA), absorb it much faster.

When damp filament reaches the hot nozzle, the water inside turns to steam. The result is small pops, uneven flow and a rough surface. Moisture can also weaken the bond between layers, so a part that looks fine may break more easily than expected.

• Crackling or small popping sounds while printing.
• A faint wisp of steam from the nozzle.
• Bubbles, roughness or tiny holes on the surface.
• More stringing than before, with unchanged settings.
• Weak bonding between layers; walls that separate easily.
• With PLA, filament that snaps on the spool or in the feed path.

Drying is always more work than keeping moisture out in the first place. A few habits prevent most problems:

• Keep spools you aren't using in a sealed, airtight bag or box with desiccant.
• Don't leave the spool on the printer once a job is done; put it back.
• Add a humidity indicator to the box. When the desiccant is saturated, replace it or regenerate it following its own instructions.
• For long prints, feed the filament from a dry box.
• Store spools out of direct sunlight, somewhere the temperature stays fairly steady.

Drying holds the filament at a temperature below the point where it softens, for long enough that the moisture can escape. The principle is simple, but a few details decide the result:

• A filament dryer with controlled temperature is the safest route.
• Household ovens can overshoot the set value and fluctuate. Too much heat can fuse the filament together or warp the spool.
• A plastic spool can have a lower temperature limit than the filament on it; consider both.
• The time needed depends on the material, how much moisture it has taken on, and the dryer.
• Once dry, move the filament straight into a sealed container. Left out, it starts absorbing moisture again.

Print a small test part before drying, then print the same part with the same settings afterwards. The difference in stringing, surface and sound is usually easy to see.

If you have a precise scale, the difference in spool weight before and after drying can also show that moisture has come out. If nothing changes, moisture probably isn't the problem; look at the other causes in the troubleshooting guide.