Temperature Rating: 5F to -4F (-15C to -20C)Is a center zip modular system comprising of the Special Forces 1 Bag for use above freezing temperatures and the Special Forces 2 Bag. Both bags come with their own stuff sack, reinforced foot and quick release center zip, for when you need to get out of your sleeping bag in a hurry. Supplied with an extra zip baffle to allow both bags to be used together and retain the convenience of closing and opening with one quick release zip.Available for purchase as a whole system or can be built up from the various Special Forces parts. These sleeping bags are designed to be layered together to cover all conditions from freezing down to as low as -4F. When ordering the entire system it is supplied with an extra compression sack to house all components.What is a Sleep System or Combo System?To help simplify the understanding of what a 'sleep System or Combo System? is and how it works we have provided this brief write up. The Special Forces 1 Bag can be placed inside the Special Forces 2 Bag and connected together using a Zip Baffle.