Abstract: A movable thermal barrier for a two-story building having a glass wall facing in a southerly direction and comprising a thermally insulated horizontal stationary rail panel adjacent to the glass wall. A thermally insulated horizontal movable inner panel is positioned between the rail panel and the glass wall, and is movable from horizontal alignment with the rail panel to above the rail panel. A similar outer panel is positioned between the inner panel and the glass wall and is movable from horizontal alignment with the rail panel to below the rail panel. Panel mounting means supported from the building are adapted to movably support the inner and outer panels so that one may be moved above and the other below the rail panel to provide a translucent thermal barrier between the upper and lower portions of the glass wall and the inside of the building. The inner and outer panels are of similar weights so they balance each other.