Why does wet filament print badly — and why does drying fix it? The answer is water's phase change inside your nozzle.

The mechanism

Polymer chains in PA, PC, PETG and TPU contain polar groups that attract water molecules from the air. At the nozzle (200–300 °C), absorbed water flashes to steam: bubbles form in the melt, burst at the surface and create blisters, hissing and rough layers. Steam also hydrolyzes polymer chains, weakening the material itself.

Who's affected most

  • PA / PA-CF / PC: highly hygroscopic — mandatory drying
  • PETG / TPU: moderately hygroscopic — recommended drying
  • PLA / ABS: low hygroscopicity — rarely need drying

The drying science

Heat (65–100 °C) raises the polymer's vapor pressure for water, driving moisture out. Time matters: 4 h for light absorption, 8 h for saturated spools. Below 40% RH storage prevents re-absorption; desiccants protect sealed spools.

VOXFIL vacuum-seals every spool with desiccant — moisture is controlled from factory to filament.