In testing for R-values a “guarded-hot-box” refers to the test equipment and the need to prevent heat from entering or leaving the isolation chamber containing the test piece. In the case of window covering testing a “guarded-cold-box” is used to prevent heat flow through the frame on the cold side of the test piece (window side). For coverings with high R-values this area will be very cold, and the high delta T to the room means that insulation alone is impractical to prevent heat flow. A cooled air raceway around the window side of the frame is used to prevent a net heat flow into this area.