Tar paper is a heavy-uty paper used in construction. Tar paper is made by impregnating paper with tar, producing a waterproof material useful for roof construction. Roofing felt, one common type of tar paper, is a fiberglass or polyester fleece impregnated with bituminous material (tar, asphaltic bitumen); it is produced in roll form. In some cases mineral material (e.g. sand) is applied on one side to help prevent the material from sticking together while in roll form and to provide protection from atmospheric conditions. A distinction is drawn between tarred board and bitumen board.