22oz double-coated nylon the most durable weather cover material used in the industry. Nylon is always stronger than the equivalent polyester substitute. It maintains flexibility longer and can withstand, in our experience and other outdoor applications, the elements better than any fabric on the market. The sole reason polyester would be used is simple: polyester is less expensive – as much as 35 percent in some cases. Regardless of the pitch, the bottom line is this: when the margin is more important than the customer and their track program, you’ll find polyester fabric.