Whether you're an outdoor enthusiast who likes to be prepared for emergencies, or a mountaineer who travels ultra-light, the Adventure Medical Kits S. O. L. Thermal Bivvy Sack is essential backcountry gear. We like to bring it for overnights in temperatures above 50 degrees Fahrenheit, and it can serve as an emergency survival shelter in winter conditions as well. The 4-ply fabric reflects 80 percent of radiated body heat to provide warmth without bulk. The durable exterior is wind- and rain-resistant, while the lightly brushed interior surface is comfortable to the touch.