Emergency Polarshield Sleeping Bag is the perfect survival blanket that you can take anywhere! The ultralight survival blanket that can be used as a sleeping bag. which is also known as a bivvy or bivouac sack. survival blanket reflects 90% of your body heat to keep you warm. This emergency blanket fits easily into your backpack and is ideal for a Bug Out Bag or for your next camping or hiking trip. Polarshield Survival sleep bag measures 36x 84.??