Turn any Western Mountaineering semi-rectangular bag into a comfortable Two-Sleeper by zipping up to our Summer Coupler! This cotton tri-blend fabric has the same feel as the sheets on your bed. Sleeves on the underside hold your insulated pads in place. By nature of its design the Summer Coupler only works on un-hooded semi-rectangular bags. This is not a waterproof sheet, so a ground cloth is still needed. The Summer Coupler only weighs 1lb. 4oz.