Do Polyolefins Need Drying? Moisture Management

Polyolefins such as PP, AYPE, YYPE and LLDPE are not hygroscopic — meaning that, unlike engineering plastics such as PA (nylon), PET or PC, they do not chemically absorb moisture from the air. For this reason a drying oven is generally not needed before processing under standard conditions.

Surface moisture can form due to condensation on the pellet surface (for example during a sudden transition from a cold warehouse to a hot production environment), damaged/open packaging, or prolonged exposure in a very humid environment — this is not moisture absorbed into the material itself, only a surface-level condition.

Particularly in clear film or high-gloss injection-molded parts, this surface moisture can lead to visible defects such as silver streaking, bubbles or haze.

Keeping the packaging closed until the moment of processing, and protecting the pellets from sudden transitions between hot and cold environments, is sufficient in most cases. If in doubt, a short low-temperature surface drying step can be applied as an extra precaution — but for polyolefins this is not a requirement, just a precautionary measure.