Our Replacement Filters Cartridges are made of premium Polymer Active Carbon, Remove bad tastes and odors, keeping water fresh from pet fountains,efficiently protect your pet healthier 4-layer High-efficiency Filtration: The Cat fountain filters made of high quality double layer cotton, activated carbon and Ion exchange resin. Cat filters fountain can catch hair and debris, filters heavy metals, improve water quality. Every filter individually packaged and sealed to maintain high quality. Cat Water Fountain Filters only compatible with Cat/ Dog Pet Drinking Fountains . The diameter of our cat filters are 12.5cm and inner circle is 3.3cm suitable for the diameter of the card slot of cat Fountain is 12.5-13cm. How to Use Pet Water Fountain Filters: Note: To prevent the activated carbon dust from shedding into water. Please soak the cat water filters in water for 2 minutes and rinse it thoroughly under running water before using it. Then install the pet fountain filters into the cat fountain. Suggested to replace it 2-4 weeks to keep the water clean and fresh. Package List:4* Cat water fountain filter