11 oz. 50/50 Poly- Cotton Blend Probably the most popular marine fabric in the  industry. The 50/50 Polyester/Cotton haze gray Double Duck with double applied water repellent, mildew resistant, UV resistant finish. When utility  and value are important, this is your best bet on  the market. Our 11 oz. 50/50 poly/cotton covers  are warranted for a full 3 years.