Turn your 3-season sleeping bag into a 4-season bag by layering it with the Helium Emergency Bivy. Just like how you'd put a hard shell over your puffy jacket, this bivy was designed to protect your sleeping bag from the elements while trapping in warmth. Built with the best-selling, award-winning Helium fabric, this ultralight shelter system uses a simple tube-like construction and cinch closure to seal out wetness and save on bulk. Weighing in at an undetectable 9.6 ounces and packing down to the size of a beer can, the Helium Emergency Bivy is perfect for adding warmth and peace of mind to your backcountry sleep setup. FABRIC PERFORMANCE DESIGN FEATURES