Growstone GPGC1.25CF is an earth friendly, 97 percent recycled glass product. Growstone can be used as an integral medium in many hydroponic systems. Growstones are developed to provide the ideal ratio of water retention and air while at the same time being light-weight, disease free, and packaged in a 1.25-cubic foot recyclable paper bag. Great alternative to heavy, dusty Hydroton and clay pebbles. Not strip-mined like Hydroton, clay pebbles or perlite. Dust free, non-toxic and chemical free. Impossible to overwater. pH neutral and reusable.