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What's the Difference between U-factor and R-value in Energy Efficient Windows?

The biggest difference between U-factor and R-value is that U-factor measures the rate of heat transfer (or loss) while R-value measures the resistance to heat loss.

R-value is a measure of conductivity. A product with high conductivity will transfer heat quickly, like a hot pan on the stove or a single pane of glass on a cold day. U-factor, on the other hand, takes into account more than conductivity. It also is affected by the airflow around the window and the emissivity of the glass.

Tags: energy efficient windows, energycore, energycore windows, heat transfer, r-value, u-value