Pentair Pentek P Series Cartridges are manufactured from pure 100% polypropylene fibers. The fibers have been carefully spun together to form a true gradient density from outer to inner surfaces. P Series Cartridges are designed for purity; they will not impart taste, odor or color to the liquid being filtered when used within the recommended temperature limit. Additionally, the polypropylene construction provides superior chemical resistance and is not prone to bacterial attack. The coreless strength of the cartridges is achieved by sintering the many fibers into a solid matrix. P Series Cartridges are available in a wide array of sizes and micron ratings to accommodate all of your filtration needs.