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Adventure Medical Kit says:
Be prepared for the unexpected with the SOL Emergency Bivvy with Rescue Whistle and Tinder Cord. The lightest emergency bivvy on the market, weighing a mere 3.5 oz. and packing down smaller than a 12 oz. soda can. The waterproof, windproof material reflects 90% of body heat while sealed seams keep out rain, wind, and snow. Start a fire with the tinder cord included on the stuff sack. The bright orange is highly visible, and the rescue whistle signals for help. Use the SOL Emergency Bivvy as a sleeping bag or a blanket to ensure you stay warm until help arrives.