Turn Western Mountaineering semi-rectangular bags into a comfortable Two-Sleep by zipping up to their 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 works only with our semi-rectangular bags which do not feature hoods. This is not a waterproof sheet, so a ground cloth is still needed. The Summer Coupler weighs just 1lb. 4oz.