# What does R-Value and U-Factor mean?

R-Value is a term that measures the insulation properties of a material. For example, fiberglass insulation is measured by ‘R-Value’. The energy efficiency of windows is measured by ‘U-Factor’. Because windows are not insulators by design, they cannot be measured in ‘R-Values’. However, windows obviously have insulating properties, so there needs to be a measurement that allows comparison of styles and window packages. There is a relationship between R-Values and U-Factors. Whereas the higher the R-Value, the greater it’s insulating ability, the lower a U-Factor, the better that product’s insulating efficiency. To find a U-Factor, divide the number ‘1’ by the R-Value. For example, an R-Value of ‘4’ is equal to a U-Factor of .25.

R-Value is a term that measures the insulation properties of a material. For example, fiberglass insulation is measured by ‘R-Value’. The energy efficiency of windows is measured by ‘U-Factor’. Because windows are not insulators by design, they cannot be measured in ‘R-Values’. However, windows obviously have insulating properties, so there needs to be a measurement that allows comparison of styles and window packages. There is a relationship between R-Values and U-Factors. Whereas the higher the R-Value, the greater it’s insulating ability, the lower a U-Factor, the better that product’s insulating efficiency. To find a U-Factor, divide the number ‘1’ by the R-Value.