These filters consist of a supporting shell, usually made of perforated sheet, and a filtering layer of fine technical cloth either on the outside or inside of the filter (depending to the direction of the flow of the medium). There can be several filtering and supporting layers. The filter can have either a solid or filtering bottom and is equipped with a flange for installation in the filtering system. It can also be equipped with handles for easier manipulation. The most common materials are DIN 1.4301 and DIN 1.4401.