Fits iSpring under sink ultra filtration system CU-A4. Official 3rd-stage replacement filter cartridge for this iSpring under counter water filter system. KDF media (or Kinetic Degradation Fluxion Media) with activated carbon. KDF removes chlorine, rust, unpleasant taste/odor and more. When used with carbon, KDF can greatly extend the carbon filter life. Individually wrapped to keep freshness. 1/4" Quick-Change connections. Easy filter change. our worry-free shopping experience is backed by a 30-day money-back guarantee, extended warranty upon registration, and lifetime tech support from iSpring in Atlanta.