The HIGHER the better. The higher the R-Value, the better the window conserves thermal energy inside the house. R-Value is a measure for how much resistance there is for thermal energy leaving or entering a home. Windows help preent thermal energy from escaping; therefore, help conserve the energy used to heat or cool a home or commercial building.
The LOWER the better. The lower the U-Factor, the better the window is at keeping heat inside the house. U-factor measures how well a product prevents heat from escaping. The rate of heat loss is indicated in terms of the U-factor (U-value) of a window assembly. U-Factor ratings generally fall between 0.20 and 1.20. The lower the U-value, the greater a window’s resistance to heat flow and the better the insulating value.
Learn more about energy efficiency.