Thickness of Spray Foam Insulation vs. Fiberglass

R-value

• The R-value is the most important consideration when choosing a type of insulation. The R-value is the measure of thermal resistance, or effectiveness. The thickness is a consideration in the calculation of the R-value, but it also takes into account the type of insulation, its properties and the density. The higher the R-value, the more effective the insulation.

Considerations

• Local and state authorities have building codes that include minimum R-values that are required for new homes constructed within their jurisdictions. The United States Department of Energy also has insulation recommendations based upon climate zones. You can combine different types of insulation to reach a desired R-value economically.

Spray Foam Insulation

• Spray foam insulation (SPF) has become known as the king of the green-building industry. SPF is a polyurethane material that delivers a high R-value of 6 in just 1 inch of the foam. The thickness of SPF is not what has earned it the accolades of home builders. Instead, it is the foam's ability to fill even the tiniest crevice.

Fiberglass

• Fiberglass insulation is made of blankets of fiberglass. The rolls or panels come in a wide variety of widths, lengths, thicknesses and R-values. A panel of fiberglass insulation with an R-value of 11 is approximately 3 1/2 inches thick; a panel with an R-value of 49 is approximately 15 1/2 inches thick. Fiberglass insulation can be layered, adding the R-values together. However, it should never be pressed together. Doing so would reduce the R-value.