iSpring F4-CUA4 Replacement Filter Pack for 4-Stage Ultra Filtration System CU-A4, Sediment, UF, KDF, and Activated Carbon Filter, 4pcs4 Stage Filter Replacement Pack: PP Sediment Filter ((5 microns) removes larger particles like rust, sand and dirt.) Ultra Filtration Filter (contains hollow fiber membrane technology with a pore size of just 0. 1 micron.) KDF and GAC Filter (provides much better control of particularly problematic contaminants including bacteria, chloramine, hydrogen sulfide, metals, and other organic compounds.) Fine Activated Carbon Filter (provides final polishing