Plastic granules are subjected to varying temperatures in storage and when being transported. Through the condensation of the atmospheric humidity on the surface of the granules, moisture may be absorbed by capillary action, depending on the time of year, the weather conditions and the type of plastic involved. For high quality end-products, the maximum limits for moisture in the granules must not be exceeded. In basic systems, drying is performed by hot air dryers, while more efficient plants employ dry air dryers. In the latter case (and by contrast with hot air drying), the processing air is carried in a closed circuit and is directed through the material (granules or powder) for the purpose of drying it. A dehumidifier (molecular sieve), positioned in the return airflow, removes the moisture in the atmosphere. In this way, a constant flow of pre-dried air is always available in the approach to the dry silo. The air is conveyed by a blower. Most modern dryers have two drying agent containers so that the processor need not interrupt the drying process in order to regenerate the moisture-laden drying agent. Regeneration is likewise performed by a blower.