Pentek ECP50-20BB Pleated Cellulose Polyester Cartridge 4.5" X 20" 50 Micron (Full Case)SOLD IN CASE QUANTITY (6 in a case) ECP Series cartridges are manufactured from a special formulation of resin impregnated cellulose and polyester fibers. This unique blend of materials provides a higher wet strength than regular cellulose cartridges. The 50 micron sediment filter also provides high flow rates and dirt holding capacity, while maintaining extremely low pressure drop. The media is pleated around a polypropylene core for added strength