Keep your filament dry: Why it matters

Filament spools

3D printer filament is made of plastics that slowly absorb water from the air. Even if it’s wrapped up, humidity can seep in over time. When a wet filament is heated in the printer’s nozzle, the trapped water turns to steam and causes trouble. You might hear popping sounds or see tiny bubbles as the filament extrudes, and the finished part can come out weak or defected. In this post, we’ll explain why drying filament is crucial, how moisture hurts print quality, how materials like PLA/ABS/PETG/Nylon differ, and easy ways to dry and store filament to keep it fresh.

How moisture hurts your prints

Wet filament leads to visible printing problems. In the photo below, a wet filament produced lots of stringing and fuzz between the shapes – a common sign of moisture. As the hot end melts the plastic, the water inside boils and bursts, ruining the smooth flow.

If your filament has absorbed water, you’ll notice issues like:

  • Bubbles or Popping Sounds: Moist filament will hiss or pop in the nozzle. This makes little holes or bubble-like cavities in the printed layers.
  • Stringing and Oozing: Fine strands of plastic (strings) can appear between parts of your print when filament moisture causes extra oozing.
  • Rough, Pitted Surfaces: Prints may feel rough or look uneven because escaping vapor creates tiny pits and bumps.
  • Weak or Brittle Prints: Layers may not bond well, so the part can be soft, brittle or break easily.

Each of these issues comes from water boiling inside the melt zone, disrupting the normal extrusion and adhesion. The result is a print that looks poor and may fail mechanically. In contrast, dry filament flows smoothly, giving strong, clean prints.

PLA, ABS, PETG & Nylon: Different Moisture Sensitivity

All filaments absorb moisture, but some much faster than others. As one guide notes, “Filaments like nylon, PVA… absorb moisture quickly, while others like PLA or PETG absorb much less”. Here’s how the common plastics compare:

  • PLA (Polylactic Acid): PLA is least sensitive of the four. It absorbs water slowly, so it’s more forgiving. However, even PLA will eventually get brittle or make prints with tiny bubbles if left out too long.
  • ABS (Acrylonitrile Butadiene Styrene): ABS picks up moisture more readily. Wet ABS can warp easily during printing and layers may not fuse well, leading to weaker parts.
  • PETG (Polyethylene Terephthalate Glycol): PETG is moderately hygroscopic. Damp PETG can produce stringing and surface bubbles in prints. Drying PETG is often a good idea if you see these issues.
  • Nylon: Nylon is very moisture-sensitive – one of the worst. It soaks up water from the air quickly. Printing with wet Nylon usually fails badly (bubbles, weak structure), so Nylon almost always must be dried before use.

In summary, Nylon and ABS need the most care, PETG is in the middle, and PLA is easiest. Even so, it’s good practice to keep all spools dry because any moisture can degrade print quality.