The Special Forces 1 Sleeping Bag can be used on its own or bought as a set of two, which can be zipped together to create an extreme bag for temperatures -15°C. Available for purchase as a whole system or can be built up from the various Special Forces sleeping bags. How does the complete system work? The Complete System gives you the Special Forces 1 Bag for use in above freezing temperatures and the Special Forces 2 Bag for use in temperatures right down to -10°C. Then, when you're in extreme conditions, you place the Special Forces 2 Bag inside the Special Forces 1 Bag and join them together with the extra zip baffle, so you're protected in conditions right down to -20°C. Ingenious! When joined in this way, you retain the convenience of closing and opening with one central, quick release zip. Both bags have a reinforced foot area and come with a stuff sack to keep everything together.