The Hayward SwimClear C4025 and C4030 Blue Anti-Microbial Replacement Filter is made to prevent mildew and bacteria build up on the cartridge. It has an injection-molded core made from 100% virgin ABS or PP. Our EverFlow+ antimicrobial high filament count spun-bond polyester is wrapped around the cores. The filter is capped with robust end caps made from a chlorine and mildew resistant urethane system. This time-tested process creates a filter that is easy to use and resistant to cracking and chemical deterioration.