Bio-Balls are made from high quality plastic. Bio-balls are great for biological filter media in all types of filters. Bio-Balls can be used in a number of ways either loose in a filter or you can put them in a mesh media bag for easy removal from filter for cleaning when necessary. Bio-balls because of their durable design will not compact like other popular fitler media. The sizing is 1.5" in diameter and are available in BLACK or BLUE.