The therm a rest synergy coupler is a brushed polyester sheet that provides next to skin comfort while joining two mattresses it includes two sleeves that can accommodate two large 25 x 77 in or 63 x 19 cm rectangular mats up to 4 inches 10 cm thick equipped with integrated perimeter loops the synergy coupler also mates with our blankets and quilts so you can create a luxurious double bed in the backcountry