there are several types of material dryers on the market. The kind of dryer chosen depends on the type of resin being used. Hot air dryers are the least expensive and oldest types of dryer in use. Used for non-hygroscopic resins that will not absorb moisture, they are comprised of a heater, a blower, and a thermostat. Desiccants, or dehumidifying dryers, are used for plastics that readily absorb moisture from the surrounding air, and utilize a tower, carousel, or honeycomb wheel design. The drying residence time with a desiccant dryer is between 1 and 4 hours. Newer models combine desiccating dryers with compressed air or vacuum techniques to ensure that the resins are thoroughly protected from moisture absorption