R-value

Thermal resistance or R-value is a measure of a material's ability to resist heat flow. A high R-value is desirable when choosing insulation for your home. R-values are commonly quoted in North America, whereas U-values are used more often in Europe. A U-value of 0.27W/m2K equates to an R-value of 21, while a U-value of 0.15 W/m2K equates to an r-value of 38. See U-value for more information