Before you gather the necessary items for your next home weatherization project, become familiar with this measuring tool. You may find that it is the most important tool for achieving the results you desire.

The R Value tells us how well a material insulates against cold or heat. The bigger the number, the better the material insulates because it has greater resistance to heat flow.

The U Value is a measurement of the rate of heat flow through a material. This means that the U Value tells you how well windows conduct heat and hold it. Lower numbers are better because they indicate slow rates of heat flow.

There is a mathematical relationship between the R Value and U Value that is worth noting. When you multiply an R Value by its corresponding U Value, the product is always 1.

In mathematical terms, this means that every U Value is the reciprocal of a given R Value. In practical terms, it means that if you know one value, you can find the other by dividing the value you know into 1.

Example 1:

The U Value of a window is .32, what is the R Value?
1/.32 = R Value
Answer: R Value = 3.12

Example 2 :

The R Value of a wall is R-6, what is the U Value?
1/6 = U Value
Answer: U Value = .16