All natural coconut coir fiber is plentiful and sustainable. Woven into sheets and cut to fit standard 1010 or 1020 nursery trays, coco coir makes a great growing medium for microgreens, wheatgrass and barleygrass. The grow mats are held together with a tiny amount of natural rubber to keep shape.These mats measure 9x9 inches and are designed to nest perfectly in a standard 10x10 inche grow tray.