Thermal insulation converter

The U-value is the heat flow through a building element per square metre and per kelvin of temperature difference, in W/(m²·K): lower means better insulation. The R-value is its reciprocal, the thermal resistance in m²·K/W, where higher is better; Canada calls the metric version RSI. The US insulation trade quotes R-values in imperial units, ft²·°F·h/BTU, which are 5.68 times larger than the metric ones, so 'R-20' batts are RSI 3.5. For orientation, an uninsulated brick wall is around U = 1.5, a modern insulated wall U = 0.2 or better, and a triple-glazed window about U = 0.8.