R-values and E-ratings are standards by which materials are measured for energy efficiency.
Insulation is rated with R-value with the higher R-value indicating greater resistance to heat flow. The R-value depends on the type of insulation, its thickness, and its density. When calculating the R-value of a multilayered installation, add the R-values of the individual layers. Installing more insulation in your home increases the R-value. You can find the recommended R-value for your area here… Insulation Guide.
However, windows and radiant barriers have an E-rating. This rating measures the ability of the material to block heat flow, minimizing heat conduction.
An E-rating tells you how much of the heat is actually going to come through. An R-value tells you how long it will take the heat to come through. Insulation does not stop heat transfer – just slows it down. Anything that has an E-rating is to block heat transfer and anything that has an R-rating is to simply slow the heat transfer. So don’t get the two crossed up, because they are not interchangeable. You have to watch the products that you are buying.
In general for R-value you are looking for a higher number for a better insulating performance. For E-ratings you are looking for a lower number indicating a smaller amount of heat that can come through.
