American Hydrotech’s Garden Tray GT15 is made from recycled polyethylene and is intended for use in a Hydrotech Garden Roof Assembly. Each molded tray includes retention cups on the top side, drainage channels on top and bottom, and perforated domes for ventilation and evaporation. In the bottom of each tray is a layer of Systemfilter fabric, which is then topped with growing media and plants. The trays measure 18" by 22" and can butt together or be mechanically fastened to each other to cover the roof area.