70 Denier Nylon with Waterproof Backing, Finally, a sport bag that is made for the outdoors Unlike most polyester gym bags that seem to just absorb any rain or moisture, this Woodcrest Sport Roll Bag is constructed of 70 Denier Nylon with Waterproof Backing to help keep your gear dry. It also has a full length front zipper pocket to keep certain possessions from getting buried in the bottom of the bag or smelling like those sweaty socks.