The best bivy sack is the Tennier Woodland Camouflage Waterproof Bivy Cover. The product is made of breathable fabric and with all seams getting heat-sealed. The bivy cover is ideal for the Patrol and Intermediate Cold Weather sleeping bags. It can fit comfortably inside the compression stuff bag and weighs just less than 3 pounds. If you believe in getting a strong body, rest assured since it gives Military Modular Sleep System for you. The waterproof Gore-TEX material is worth taking along anywhere.