The Alpinist Bivy by Marmot weighs in at under a pound (14 ounces) making it highly compressible so that it can pack right into your back pack. The Alpinist Bivy (27720) by Marmot will offer climbers and avid outdoorsman a little extra protection from the elements with a storm flap, and built with Marmot MemBrain fabric that is waterproof that is breathable while still blocking out the nasty elements around you. The Alpinist Bivy by Marmot is fully seam taped, making this bivy 100% waterproof, durable and breathable.