Zilla Replacement Filter Cartridges are dual-sided, featuring fibers made from sustainable materials infused with carbon. This sustainable material allows these cartridges to be EcoFriendly being both biodegradeable and compostable. The EcoRenew cartridges also feature a NoDrip design to help eliminate extra water mess when changing your filter cartridges. Due to the sustainable nature of the EcoRenew (TM) cartridge, it is recommended to replace BEFORE is starts to decompose-approximately 4 weeks.