Nylon is hygroscopic, which means that the material both receives and emits moisture. When parts are bagged, water is added to the bag and it is sealed to allow the water to get soaked into the part. The parts need a certain amount of time before the moisture gets soaked into the part, which is called “curing time.” Most parts have a curing time of one or two days, but some can take up to 3-4 weeks. Nylon does darken or “yellow” with age, but this does not affect the performance of the parts.