3-Layer Filtering: Water quality can be improved by the 3 types of filtration. The external nylon layer on each filter captures hair and debris. Three steps of filtration can assure the quality of the water and enhance the taste of fresh water for your cats. Dual-Action Filters: Resin and active carbon. Resin can soften water and reduce the chance of lithiasis. Activated carbon can adsorb impurities and odor, keep the water fresh and clean. Pack and Size: Value pack of 4 filters. Compatible with PingPin water fountain. Size: Diameter: 9.9cm/3.9in; thickness: 8mm/0.31in. Easy to Use: Rinse the filter with water thoroughly before using, easy to mount it on pet water fountain. In order to ensure the water clean, the filter should be replaced in time, please replace them within 2 to 4 weeks.