Instead of the leak-prone overlap-style opening of other bivy sacks, we gave ours a long, circumferential zipper opening which is much more weatherproof. We've also added snaps around the storm flap. They make it easy to snap the roof in place to keep the rain out but still allow the zipper to be left wide open for maximum ventilation. We use the most vapor permeable Gore-Tex available, and it covers nearly everything save for the floor, which is a taffeta nylon that's coated with our exclusive Hydroseal-200® coating for the ultimate in waterproofness. Our sleeping pad straps enable you to lock your sleeping pad in place to prevent the bivy from tossing and turning while you do, and no-see-um netting keeps out the little buggers while you star gaze.