Terms of the Trade: What Is R-value?
R-value is a measurement of heat resistance through a material. The higher the R-value, the more effectively it insulates against heat per inch of thickness. This measurement is used primarily when discussing insulation and energy efficiency in people's homes. Keep in mind that installing two sheets of insulation in a given area back-to-back instead of only one will not double the R-value, though it will increase it slightly.