Filament Moisture Absorption Calculator

Why filament absorbs moisture: Most 3D printing filaments are made from hygroscopic polymers — materials that naturally attract and absorb water molecules from the air. This is especially true for Nylon, PVA, and TPU, but even PLA can absorb enough moisture in humid environments to noticeably 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 has been exposed to very high humidity for extended periods, the polymer chains themselves can break down through hydrolysis — a chemical process that heat-drying cannot reverse. Brittle, crumbly filament that snaps easily has likely undergone hydrolysis and should be replaced.