R-values represent the thermal resistance (transfer of heat) through materials and/or assemblies. The higher the value of R, the better thermal performance relative to resistance (convection and radiative) of heat moving through the material/assembly. R-values do not account for the radiative or convective properties of the materials, surface.
R-values are the inverse of thermal transmittance (U-value) of a material/assembly. R-values are easier to calculate for assemblies and are scalable for varying thicknesses of a material. R-values expressed in United States customary units are about 5.67 times larger than those expressed in metric (SI) units.
