What Insulation R-Value Means

The R-value of commercial insulation measures the resistance to thermal transfer. It is the product of an insulator’s material thickness and its density. The higher the R-value, the greater its thermal resistance and insulating capability. R-values are measured under certain conditions to provide a comparison of performance between different materials. R-values are additive for layers of insulation, but they do not apply to whole wall assemblies or windows, which have their own R-factors, called U-factors (U-value).

R-Value is a measure of thermal resistance per inch of thickness and varies by material type. Vacuum insulated panels and aerogel have the highest R-values, followed by phenolic foam, polyurethane (PUR), polyisocyanurate, and expanded and blown cellulose.

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Depending on the location and structure of your home, the Department of Energy recommends specific R-values for each region. The R-value of insulation is also dependent on your climate as it affects how much heat and cold you need to stay comfortable.

While R-values are useful in comparing the performance of insulation products, they only apply when the insulation is properly installed. For example, stuffing two layers of fiberglass batting into a wall cavity sized for one layer will not double its R-value because the compression of the second layer changes the insulating characteristics of the first.

Even correctly installed fiberglass and cellulose insulation can lose R-value due to gaps between the insulation and framing members such as studs, doors, and window frames. Adding RetroFoam injection foam insulation can eliminate these air gaps and increase the overall R-value of your home’s insulation.

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