U-value and R-value

What do U-value and R-value mean?

High-performance windows are designed to insulate homes against heat gain or heat loss. Homeowners prefer windows that insulate extremely well and improve the overall comfort of a home and room. How well a window insulates is measured as the U-value.

The U-value measures how much heat will transfer through a window. The lower the U-value, the better a window insulates by means of reducing heat flow and maintaining comfortable temperatures.

The R-value is the opposite of the U-value; it depicts a windows total resistance to heat loss. The R-value is used mainly to compare windows with walls, insulation, and other home fixtures. The higher the R-value, the greater resistance a window has to heat loss.