This R factor corresponds to the relative motions occurred during molecular dynamics (see more at flexibility ).
Energy efficiency in windows is rated by two factors: The U-factor and the R-factor.
The R-factor measures the resistance of heat transfer of certain materials.
For the R-factor, the higher the number means that the materials are insulated better.
If a window has a high R-factor and a low U-factor then this window is very energy efficient, which drives up the price.