State-of-the-art glazing systems can provide very good solutions for cold climate conditions, and fairly effective ones for warm climates. However, there is still no window system on the market that can offer the flexibility required to provide a comfortable visual environment and an efficient energy response in climates where heating is required in winter, and cooling is required in summer. This paper describes an experimental investigation of a novel glazing system, designed to overcome glare and radiation damage to interior furnishings, yet which causes no reduction in the energy efficiency of the glazed opening compared with a conventional window used in direct gain systems. The proposed glazing system (patent pending) incorporates a rotatable frame holding two glazing components: transparent glazing providing a weatherproof seal, and absorptive glazing with a low shading coefficient1A patent application describing the window was filed with the Israel Patent Office in November 1997. The absorptive glazing is fixed at a small distance from the clear glazing, forming an airspace between them which is sealed at the sides but open at the bottom and top, so that air flows freely through it. In summer, the absorptive glass faces the exterior of the building, absorbing excessive solar radiation and dissipating the heat to the ambient air. In winter, the glazing assembly is rotated so that the absorbing glass faces the interior, reducing glare but allowing effective convective and radiative heating of the adjacent space.