Pentair Pentek 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. It 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. The pleated endcaps of the standard cartridges are immersed in a thermo-setting vinyl plastisol. The Big Blue cartridges have a molded endcap with gaskets. The pleated ends are sealed to the endcap with a thermoplastic adhesive. The overlap seam is sonically welded to reduce internal bypass, improving filtration efficiency. ECP Series Cartridge endcaps feature a color-coding system for easy identification of micron ratings: tan (1 micron), white (5 micron), blue (20 micron), and yellow (50 micron).