There is disclosed a window shade system which reduces heat transport through windows by providing an insulating seal between a shade and window sill. The insulating seal is effected by a resilient material attached to the bottom longitudinal edge section of the shade. When the bottom longitudinal edge section of the shade is positioned in engagement with the sill, the resilient material conforms to the contour of the sill, frictionally sealing the shade against the sill, thereby insulating and reducing heat transport through the window. In a preferred embodiment of the invention, the bottom longitudinal edge section includes a first depending longitudinal slat pocket for receiving a window shade slat, and a second depending longitudinal pocket configured to substantially enclose the slat pocket. A longitudinal void is provided between the pockets to permit the enclosing pocket to resiliently conform to the contour of the sill.