The Filters Fast® FF-0421 Replacement for Filbur FC-0420 is used to purify swimming pool and spa water. The Filters Fast® FF-0421 Replacement for Filbur FC-0420 pool filter is constructed with reinforced PVC center cores that provide strength and support while reducing the likelihood of cracks or collapse. The polyester media of this compatible Coleman filter features sharp pleat folds that trap dirt and other particles found in water. In addition, the antimicrobial end caps of this pleated pool filter cartridge reduces bacteria and mold build-up.