Oil Absorbing Filter Bags Filter bags for liquids are effective in removing particulate contaminants in the processing of a wide variety of materials. Such units typically consist of a simple filter housing, a retaining basket and the filter bag Woven filters are made of yarn with a definite repeated pattern. Felted filters are composed of randomly placed fibers compressed into a mat and attached to loosely woven backing material. A membrane filter is a special treatment where a thin, porous membrane is bonded to the scrim or support Fabric