Regenerative desiccant type dryers use a porous desiccant that adsorbs the moisture by collecting it in its myriad pores, allowing large quantities of water to be retained by a relatively small quantity of desiccant. Desiccant types include silica gel, activated alumina, and molecular sieves. In some cases, more than one desiccant type can be used for special drying applications. In most of these cases, a larger particle size (1/4” or more) is used as a buffer zone at the inlet, while a smaller particle size desiccant (1/8” to 1/4”) is used for final drying. Where very low dew points are required, molecular sieve desiccant is added as the final drying agent. The most common dew point rating for these dryers is -40. While this level may be needed for sensitive processes or instrumentation, this level of dryness in not normally needed in general manufacturing unless the pipes are exposed to freezing temperatures.