Insulation: Are All SPFs Created Equal?

April 3, 2006
There are three types of SPF commonly used within the construction industry

You probably don’t spend a lot of time thinking about chemistry when you consider adding insulation to improve energy efficiency. Yet one popular insulation material - spray-applied polyurethane foam (SPF) - relies entirely on chemical cleverness.

Not all foams are created equal. Spray-applied polyurethane foam is a two-component product that is manufactured on-site but engineered at the molecular level to optimize performance for a specific application. By varying key components, the finished product can be modified to meet specific performance requirements for roofing applications, insulating air barrier systems, adhesive applications, or wall insulation.

Currently, three types of SPF are commonly used within the construction industry:

  • Medium-density (MD) 24 kg/m3 to 48 kg/m3 (1.5 pcf to 3 pcf).
  • Low-density (LD) 8 kg/m3 to 12 kg/m3 (0.5 to 0.7 pcf).
  • Sealant foams.

The most important distinction is whether the formulation produces an open-cell or closed-cell foam. MD foams are formulated to have a closed-cell content of greater than 90 percent combined with an effective R-value of over 6.0 per inch. LD open-cell foams have approximately 60-percent open-cell content and offer an R-value between 3.0 and 3.6 per inch. But, R-values are only the beginning when it comes to energy efficiency. It is the air-permeability capabilities that are the true differentiator.

Yes, you need insulation; but, in order to make a building truly energy efficient, you need an effective, continuous air barrier system. Without it, conditioned air escapes through the building envelope and the HVAC system has to work harder to keep the indoor environment comfortable (see Air Barriers Go Legit, right).

Most open-cell foams have not been tested and, therefore, do not qualify as air barrier systems in “typical thickness” of less than 4 inches. One open-cell foam manufacturer’s product requires an application of 5.5 inches (its maximum allowable thickness) to pass the minimum requirements of ASTM Intl. E 2178, Standard Test Method for Air Permeance of Building Materials (air-leakage rate of 0.005 L/s/m2 at 75 Pa). Compare this with closed-cell foams, some of which provide air-leakage rates of <0.001 L/s/m2 at 75 Pa at 1.5-inch thickness.

Because the systems are spray-applied, fully adhered, and seamless, they also eliminate connective loops behind the insulation and, therefore, eliminate moisture. Since mold requires three things to grow - moisture, warm temperatures, and a food source - and closed-cell foams do not provide any of these things, MD closed-cell SPF can help prevent dangerous mold infestations.

Open-cell foams offer a slight cost advantage when compared on an equal-thickness basis and, in general, provide greater sound control. On the other hand, closed-cell formulations can actually improve building durability and structural strength. Both closed-cell SPF systems and open-cell foams provide environmental responsibility, have no adverse effect on the ozone layer, and do not emit volatile organic compounds.

Tom Harris is the product manager for Minnea­polis-based BASF Polyurethane Foam Enterprises LLC (

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