The Black Diamond Winter Bivy was designed both as a minimalist bivy sack and a winter sleeping bag cover. Great for keeping down sleeping bags dry in wet coastal climates. Extremely lightweight, this innovative bivy sack is made of a breathable silicone encapsulated polyester ripstop fabric. This fabric allows the Winter Bivy to pack down so small that it can be carried in the pocket of your jacket. Ideal for protection in all conditions, the Winter Bivy can also be carried as an emergency shelter for climbers, hikers, and bikers out on day trips. During the summer months, you can use the Winter Bivy as a lightweight alternative to a sleeping bag. Zippered entry across the shoulders is conveniently positioned for easy access and sitting up.