Pentek WPX100BB97P Fibrillated Polypropylene String-Wound Cartridge 4.5" X 10" 100 Micron (Full Case)SOLD IN CASE QUANTITY (8 in a case) WPX BB Series Cartridges are manufactured in 10" and 20" lengths and in 4. 5" diameters from a durable polypropylene cord that is wound around a rigid polypropylene core. The WPX BB Cartridges are an economical solution to reduce fine sediment including rust, sand and scale particles. The material in the WPX BB Cartridges is a fibrillated polypropylene media wound in a precise pattern around a polypropylene core,