People are always asking what are the best tarps to block the sun there are 2 types of tarps for this of application. The silver tarps and silver/black poly tarps. The silver tarps are the way to go. Our silver tarps are super heavy duty and great sun inhibitors. All of our heavy duty poly tarps are UV treated but the silver application that is applied to the tarps simply creates a reflective sheen on the tarp material. The silver/silver tarps (which is a tarp that is silver on both sides) enables to have a reflect ant on both sides of the material. The silver/black tarps have silver on one side and black on the other side of the tarp. The black side of the tarp acts as a light inhibitor thus blocking out light better than other tarps due to the silver reflective on one side of the tarp and the black out material on the other side of the tarp. While some people might use a dark green tarp for shade the ultimate sun blockage would be one of our silver poly tarps.