The Hay Cover is an extra heavy duty tarp that is reversible. Put the white side out if you want to reflect the sun's heat and keep things cool. Put the black side out and it will retain more heat. This tarp is popular for covering hay (blocking sunlight prevents germination). Made of polyethylene, this tarp has maximum ultraviolet-inhibiting (UVI) additive in the inner woven material and the coating, which allows it to last much longer in direct sunlight than similar tarps. The Hay Cover has grommets every 18 inches on all sides. On the two longer sides, it also has web loops every 36 inches. This provides two options for securing the tarp in place. The Hay Cover also has sewn, reinforced corners and a heavy duty 5mm rope in the hem. The material of the Hay Cover is 14X14 weave (14 threads of polyethylene either direction in each square inch) and approximately 14-15 mil thick. The approximate finish size of this tarp is 23'4" x 34'9" due to its hems and seams.