The military GORE-TEX® woodland camo bivy cover is the outer layer of the 3 piece sleep system. The woodland camouflage outer is lined with genuine goretex for waterproofing. This outer shell is a great way to add an extra layer of protection for any type of mummy sleeping bag that you may currently own. It is generous in size at 30″ x 80″ and only weighs in at 2 lbs. 3 oz. so it wont weigh-down a good lofting feather bag. it can repel frost and rain and dew. it makes a good moisture barrier for the ground as well. The bivy cover zips along the full length of the bag with a quality zipper. A windproof zipper cover can be snapped along the sipper route as well to really seal in the heat. These snaps come in handy in case the zipper ever fails.