20 x 38 Silver Color 12 Mil Heavy Duty Tarp / Canopy. 12 Mil is a Heavy Duty Premium Poly Tarp / Canopy that offers durability and versatility, whether you use it as a car cover, to rake leaves, as a tent base or to cover your lawn mower. The 12 mil polyethylene tarp is three-ply, waterproof and resistant to the sun’s UV rays. It’s also rot proof, acid resistant and almost impossible to tear. Made with rope reinforcing around the edges and aluminum grommets spaced every 18 inches apart. Finished size is 6 shorter.