uPVC WINDOWS - R-VALUE
R-Value is a measure of thermal resistance. The higher the number for an R-value the greater the insulation. In America R-value is measured in square feet fahrenheit hours per British Thermal Unit (ft2 F h/Btu), whereas in Europe the metric measure is square meter kelvins per watt (m2 K/W). Often an R-value is just expressed as a number and only through the magnitude of the number can you dedudce which unit of measurement is being used.