Descriptions: Activated carbon can absorb impurities and peculiar smells, to keep the water fresh. PP cotton can filter out hairs, sands and debris, to purify the water. Specifications: Name: Cat Drinking Fountain Filter Inside Material: activated carbon Dimensions: Outer Diameter: about 10.5cm/4.13in Inner Diameter: about 2.7cm/1.06in Thickness: about 10mm/0.39in Packing List: 4*Cat Fountain Filter Notes: Due to the lighting effects and shooting angles, there is color difference in the product, please understand. Due to manual measurement, there is tolerance in the product size.