This is a 4 piece sleep system that was used in the US Military. The sleep system contains two sleeping bags, a waterproof bivy cover, and a stuff sack. The intermediate sleeping bag protects the user from cold weather. The patrol bag keep the user comfortable in warmer weather, up to 50 degrees. You can combine the two bags with the bivy-sack. When used in conjunction with cold weather clothing, you can sleep in extreme cold weather environments. In fact, the user can sleep in temperatures down to -30 degrees. All of the components fit in the large stuff sack for easy storage and carrying.