The Pentair Pentek NCP-20BB is a 20-inch pleated cartridge built from carbon-impregnated non-cellulose polyester media. It combines sediment filtration with chlorine taste and odor reduction in a single cartridge, at a nominal 10 micron rating, for cleaner and better-tasting whole house water. Unlike cellulose dual-purpose cartridges, the non-cellulose media can be used with both municipal and non-chlorinated water, so it is an excellent polishing filter for well water and for post-reverse-osmosis systems. The pleats add surface area for high dirt-holding capacity while keeping pressure drop low, about 1 psi at 10 gpm, and the combination of pleated polyester and carbon filtration produces a long service life. It is rated for water up to 125 degrees F. The 20" x 4.5" cartridge fits Pentair Pentek Big Blue and other heavy duty housings and replaces most 20-inch carbon cartridges. Replace every 6 months or when you notice a drop in water pressure or a return of chlorine taste and odor. This listing is a Pack of 2.