The Cocoon Silk MummyLiner Coupler works as a solo sleeping bag liner or travel sheet, or it can be zipped to any other Cocoon TravelSheet for a two-person system. Zip the Silk MummyLiner Coupler to a Tropic Traveler sleeping bag to make it into a two-person sleeping bag for warm-weather camping. Cocoon made this versatile liner bag from silk material for incredible comfort in camp or during your travels.