Filament Moisture Absorption Calculator

Why filament absorbs moisture: Most 3D printing filaments are made from hygroscopic polymers, meaning they attract and absorb water molecules straight out of the air. Nylon, PVA and TPU are the worst offenders, but even PLA picks up enough moisture in a humid room to visibly degrade print quality.

Symptoms of wet filament:

• Popping or crackling sounds during printing (water vaporizing in the hotend)
• Increased stringing and oozing between parts
• Bubbles or foam texture on the surface of prints
• Rough, matte finish instead of smooth glossy surface
• Reduced layer adhesion and brittle prints
• Steam or visible vapor coming from the nozzle

The 24-hour rule: Most filaments left open in ambient air above 50% relative humidity for 24 hours or longer will absorb enough moisture to affect print quality. Nylon and PVA can become problematic in as little as a few hours in humid conditions.

Material moisture sensitivity:

• PLA: Low sensitivity. Safe below 45% RH. Can usually be stored open for a few days without major issues.
• PETG: Medium sensitivity. Safe below 30% RH. More hygroscopic than PLA, store sealed between print sessions.
• ABS: Low-medium sensitivity. Safe below 40% RH. Less moisture-sensitive than PETG.
• TPU: High sensitivity. Safe below 20% RH. Wet TPU strings badly and loses elasticity.
• Nylon: Very high sensitivity. Safe below 15% RH. Absorbs moisture in hours and degrades structurally.
• PVA: Extreme sensitivity. Safe below 10% RH. Can dissolve if left in very humid air.

Drying methods:

1. Oven: Lowest cost. Set to the recommended temperature, always verify with an oven thermometer, as many ovens run hotter than displayed.
2. Food dehydrator: Excellent temperature consistency, designed for long gentle heat cycles. Popular in the maker community.
3. Commercial filament dryers: Purpose-built devices like PrintDry, eSUN eBOX, or Creality Filament Dryer. Many allow printing directly from the dryer.
4. Dry box: Airtight container with desiccant (silica gel). Prevents moisture absorption rather than removing it.

Prevention is easier than drying: Store filament in sealed bags or airtight bins with fresh silica gel desiccant. Replace or regenerate desiccant when it changes color (indicating saturation). Vacuum-sealed bags with desiccant inside are the gold standard for long-term storage.

Signs of irreversible degradation: If Nylon or PVA sits in very high humidity for a long stretch, the polymer chains themselves break down through hydrolysis, and no amount of heat-drying reverses that. Filament that has gone brittle and snaps when you bend it has almost certainly hydrolysed, and belongs in the bin rather than the dryer.

How the risk score below works. One number drives everything: how far your humidity sits above the material’s safe limit, plus how far your storage time runs past its safe window, plus a penalty above 30°C. The four risk bands are cut-offs on that same score, so the verdict in the panel and the curve in the chart cannot disagree with each other. A material’s safe window is what makes the difference: 30 days for PLA against half a day for PVA, so the same shelf treats them completely differently.

Ambient humidity is not the whole story. A sealed bag with fresh desiccant sits somewhere near 10 to 20% regardless of the room, which is why the prevention advice matters more than the drying advice. Enter the humidity inside the container if that is where the spool lives, not the number on the wall.