A high R-rating window assembly storing multiple, reciprocating reflective flexible film layers in a sealed housing between rigid (e.g. glazed) layers. The glazed layers are separated on the order of 3 to 5-inches and are secured to low thermal conductivity framework pieces. The framework is capped with a motorized roller and film housing and the assembly is evacuated and filled with a desiccated, inert dry gas. Several plastic, reflective coated films are supported under tension in planar parallel relation between the glazing layers from the motorized roller and several guide rollers and guide tracks. Location sensors responsive to indicia on the films identify film position. Temperature sensors monitor ambient, internal and user set thermal conditions to control film exposure. The films are operable via a room control system and window controllers to define open, closed and partial exposure conditions. Alternative control functions may control film exposure in relation to room occupancy.