The supporting layer of a cylindrical filter is usually made of a stronger wire screen or perforated sheet. The filtering layer of technical cloth is either on its outer or inner side (depending on the direction of the flow of the medium). The filtering layer can be equipped with another protective screen layer to prevent damage during manipulation or in case of the back flow of the medium. The edges of the filter may be reinforced. The most common materials are DIN 1.4301 and DIN 1.4401.