The Marmot Alpinist Bivy is a waterproof/breathable bivouac sack for the twenty-first century. The Alpinist Bivy is 100% seam taped for waterproofness and durability, weighs in at under a pound, and compresses like magic into any pack. High-tech Marmot MemBrain® fabric breathes easily while blocking wind and water: The Alpinist Bivy offers awesome minimalist protection for climbers and backcountry adventurers who must travel light. No need for a tent! Experience the outdoors as fully as you can - and still stay warm and dry!