There are plastics (like Polyamide) which are brittle in the dry condition (water proportion < 0.2 %).
The plastic part gets more elastic when water up to 3.5 % is absorpt.
The storage and water absorption in moistured athmosphere or in a water bath until the weight is consistent is called conditioning.
The conditioning occurs by diffusion and may take several days.
The process is reversible.
This glossary of plastic industry is provided by PLEXPERT Canada Inc.