Suitable Size: The round compost bin filters are approximately 17 cm in diameter and 5 mm thick, a universal size. Pack of 8: One pack contains 8 activated carbon filters. One filter typically lasts about 2 to 3 months. This also depends on what is put in the compost bin. Compost, weather, and many other factors can affect air quality, so it will only take a few weeks. Quality Material: These compost filters are made of activated carbon, tear-resistant, and safe to use. Freshness: Absorbs and traps food odors inside the compost bins. Compost gives you fresh and clean indoor air. Easy to Use: Simply slide the filters into the compost bin lid, very convenient to use.