The Pentair Pentek P1 is a fine 1 micron spun-bonded polypropylene sediment cartridge made from pure 100% polypropylene fibers. The fibers are spun together to form a true gradient density from the outer to inner surface, trapping coarse particles on the outside and finer particles deeper within. This reduces fine dirt, sand, silt, rust, and scale, helping protect your appliances, plumbing, and downstream filters such as reverse osmosis membranes and carbon blocks. Designed for purity, the cartridge will not impart taste, odor, or color and provides superior chemical resistance for both chlorinated and non-chlorinated water. The coreless cartridge is sintered into a solid matrix for strength, and is Tested and Certified by NSF International to NSF/ANSI Standard 42 for material requirements. With maximum dimensions of 2.38" x 9.88", this cartridge fits standard 10" x 2.5" housings and has an initial pressure drop of just 0.6 psi at 5 gpm over a 40 to 145 degrees F temperature range. Replace the cartridge when you notice a drop in water pressure or water quality.