The rising cost of energy makes it easy to understand the growing popularity of spray-foam insulation. Filling a home’s walls and ceilings with expandable spray polyurethane-foam (SPF) insulation is an easy way of obtaining a tight, well-insulated envelope. Two types of spray-foam insulation are available: closed-cell and open-cell products. Each type of spray foam has varying insulating qualities and applications.

Open-cell foam expands 100 times its volume, which is much greater than the expansion rate of closed-cell foam. This means that less material needs to be applied to fill wall and ceiling cavities, which reduces costs and conserves resources.

However, the R-value of open-cell foam might not be great enough to offer code-compliant R-values when used in 2×4 walls.

Extra insulation could be needed even though studies have proved that open-cell foam works better than code-compliant batt-filled walls.

Open-cell foam, which uses water as its blowing agent and retains a consistent R-value, is vapor permeable, so it’s best used in wall and roof assemblies that need to be allowed to dry.

Unlike closed-cell foam, open-cell foam expands in the direction of least resistance, which makes it suitable for insulating existing walls without blowing out drywall and interior finishes.

R-value: 3.5 to 4 per in.
Density: 0.5 lb. per cu. ft.
Cost: 35¢ to 55¢ per bd. ft.

Closed-cell foam is denser than open-cell foam and has a higher R-value. It is also more rigid. Studies have proved that closed-cell foam adds shear and racking strength to wall assemblies, a benefit unattainable with open-cell foam. Closed-cell foam’s low perm rating means it is highly resistant to moisture absorption.

HCFCs (hydrochlorofluorocarbons) are no longer used as the blowing agent in closed-cell foam; a different non-ozone-depleting gas is. Off-gassing is an issue with closed-cell foam, and its initial R-value will diminish slightly over time.

Besides its use…