What is the difference between R-value, which is often cited in insulation literature, and U-value, which I see in the published material concerning windows?
R-value and U-value are two sides of the same coin essentially. The term R-value is, as you state, usually cited when discussing such things as wall and ceiling insulation value. The term does not translate well to windows and other fenestration products. The industry prefers U-value, instead. These are actually inverse terms. The higher the R-value, the better insulated are walls and ceilings. The lower the U-value, the better job a window does in keeping out heat and cold.
