The bivi bag is made without a zipper. It is made with snaps that off set those on the sleeping bag. One side is the male and the other female snap. In this manner the bivi bag can be closed if used by itself. There is a generous flap that covers the center of the bivi to keep out rain. The bivi connects to the sleeping bag with the snaps and does not impede the opening of the bag in a hurry if that becomes necessary.