Audible popping or crackling sounds during printing. The surface looks rough or bubbly. More stringing than usual. Layer adhesion seems weaker. These symptoms appear together or individually on filament that absorbed moisture from the air.
Confirm the Filament Is Actually Wet
The clearest diagnostic is sound. Put your ear near the hotend. Wet filament crackles distinctly — small pops as steam vaporizes inside the melt zone. Dry filament extrudes silently. If you hear popping that correlates with extrusion moves (louder during printing, quiet during travels), the filament is wet.
Visual confirmation: look at the extruded filament leaving the nozzle during a purge. Dry filament comes out in a smooth, consistent strand. Wet filament comes out with a rougher texture, may have small bubbles, and often looks less shiny.
Which Materials Absorb Moisture Fastest
Hours of exposure before symptoms in humid climates:
- PVA: 1–2 hours. Keep sealed at all times except when printing.
- Nylon (PA6): 2–4 hours. Always dry before printing; always use a dry box.
- TPU: 4–8 hours.
- PETG: 12–24 hours in coastal or high-humidity environments; days in dry climates.
- PLA: Days to weeks. Usually needs a month or more of open air exposure to show symptoms.
- ABS, ASA: Similar to PLA. Not very hygroscopic. Rarely the moisture issue.
Drying Temperatures and Times
Do not exceed these temperatures or you’ll deform the spool:
| Material | Temperature | Time |
|---|---|---|
| PLA | 45°C | 4–6 hours |
| PETG | 65°C | 4–6 hours |
| TPU | 55°C | 4–6 hours |
| ABS / ASA | 65°C | 4 hours |
| Nylon | 70–80°C | 8–12 hours |
| PVA | 45°C | 4 hours |
A food dehydrator at the correct temperature works well. Most kitchen ovens run too hot and vary wildly — if using an oven, verify the actual temperature with a separate thermometer. Dedicated filament dryers (eSun, PrintDry, Polymaker) hold temperature accurately and are worth the cost if you print moisture-sensitive materials regularly.
Dry Box During Printing
Drying the filament before printing and then leaving it on an open spool rack in a humid room defeats the purpose — it absorbs moisture again while printing. For Nylon, TPU, and PETG in humid climates, use a dry box: a sealed container with desiccant that feeds the filament directly to the printer. This keeps moisture below the threshold where it affects print quality throughout long prints.
When Drying Doesn’t Help
PVA that has been saturated for weeks may be hydrolyzed rather than just moist — moisture actually breaks down the polymer chains. It won’t dry back to usable condition. Discard it. Same applies to severely degraded Nylon that has gone brittle regardless of moisture content. Dry before writing off a spool, but recognize when the material is beyond recovery.