The 3 pack PETKIT Eversweet Travel Carbon Replacement Filtration units are only to be used with the EVERSWEET Travel device. The filtration units are composed of natural coconut shells and sold as a 3 Pack. The filtraion unit helps filter out Heavy Metals and Chlorine found in contaminated or unfiltered water. Internally each filter features mesh screens with activated carbon and Ion-Exchange Resins. Each Carbon filter is to be used for 100 bottles, 300 bottle supply per pack.