getting to know the "r- value"

R value insulation ratings are used to measure insulations ability to resist heat flow. The higher the R value, the more effective it is. House Insulation should be purchased based on its R value, not thickness or weight. The R-value being discussed is the unit thermal resistance. This is used for a unit value of any particular material. It is expressed as the thickness of the material divided by the thermal conductivity.

The US Department of Energy has recommended R-values for given areas of the USA based on the general local energy costs for heating and cooling, as well as the climate of an area. There are four types of insulation: Rolls and batts, Loose-fill, Rigid foam, and Foam-in-place. Rolls and batts are typically flexible insulators that come in fibers, like fiberglass. Loose-fill insulation comes in loose fibers or pellets and should be blown into a space. Rigid foam is more expensive than fiber, but has a higher R-value. Foam-in-place can be blown into small areas to control air leaks, like those around windows.