What Does an R-Value Mean?

R-ValueWhen shopping for or comparing insulation, one number you will constantly run across is the R-Value. This value is one of ways to measure the quality of insulation. In particular, it is the measurement of the ability of a single unit of insulation to resist heat transfer. Higher the R-Value, the better able the insulation is able to prevent heat escaping through the wall.

Types of Insulation

Different types of insulation will have different R-Values. Most insulation works by trapping stagnant air or other gases, reducing the ability of the surrounding material to conduct heat. With rigid foam insulation, you can double the R-Value by simply doubling the thickness of the insulation. With rolls and batts, cramming more insulation into a space will increase the resistence to heat transfer, but it will not double it. This is because increasing the density of the insulation reduces the ability to trap stagnant air, which is the main way that this kind of insulation reduces the transfer of heat. If you are uncertain about what types of insulation you require, Energy Star lists recommended R-Values based on region and use case.


Over time, the ability of insulation of resist heat transfer decreases. This means the actual R-Value of an older building will be lower than the rated value at the time of construction. Gases leak out of foam insulation over time and gravity compacts loose fill and roll and batts insulation.

Other Considerations

It is important to keep in mind that the R-Value is measured under ideal circumstances. There are other factors that will affect the ability of a building to retain heat. Areas not covered by insulation, such as windows and studs allow heat to escape. Incorrectly installed insulation, or using the wrong type of insulation for a particular job will also reduce the R-Value in practice.

The R-Value, or ability of a single unit of insulation to resist heat transfer, is an important factor in judging insulation. When considered along with other factors, such as region and energy requirements, it can help determine the best insulation for a particular job.

Related Resource: U-Value