The Quart System combines our Softie® 3 Merlin with our TS-1 Liner and Bivvi bag. It can be used as a one or two season sleeping bag. There is a waterproof housing built into the stuff sack to keep the bivvi separate after use in case it is wet, so you keep your sleeping bag and liner dry. With this system, you get all three components for a reduced price, rather than purchasing them all separate