We all come across a host of green building technical terms in our day-to-day work. If you’re new to green, you may be wondering what some of these mean. One such set of terms is "R-value" and "U-value" used to describe a material’s insulating properties. What’s the difference?

R-values measure resistance to heat flow. Higher values mean better insulating properties. The measure is typically applied to materials specifically intended to provide insulation, such as fiberglass batts, spray-foam, etc.

U-values measure a material’s heat conductivity (the amount of heat it allows to escape). The lower the value, the better the insulating property. U-values are usually used for materials other than those whose primary purpose is to insulate (windows, for example).

The two values are different sides of the same coin and are closely related. To convert between U- and R-values, simply take the reciprocal:

R = 1/U
U = 1/R

What terms do you frequently use that others may be interested in learning more about? I'd like to hear your thoughts and expertise on them.