For Premium Performance Filtration- This Aqua-Pure dirt & rust cartridge is made from an exclusive process using pure white celluose fibers. As water passes from the outer surfaces into the center of the cartridge, the filtering pores become increasingly smaller to remove even microscopic particles. Unlike string-wound and pleated paper cartridges, the rigid, sturdy construction of the Aqua-Pure cartridges are able to withstand high pressure drop and stressful conditions such as water hammer.