JUWEL Poly pad is used to catch coarse particles of dirt in the water. As a mechanical pre-filter, it protects the filter from rapid soiling and means that you don't have to clean the other filter media as often. JUWEL filter floss consists of fine, residue-free polyester material and is suitable for use in both saltwater and freshwater aquariums. Characteristics of JUWEL Poly pad: • Serves as a mechanical pre-filter • Protects other filter media from rapid soiling • Made of residue-free polyester material • Suitable for use in saltwater and freshwater aquariums • 5 filter flosses in each package