To make a building more sustainable, the insulation and air-sealing package is of paramount importance. Spray polyurethane foam (SPF) can provide the energy efficiency project teams are seeking. Among its many benefits, SPF seals the structure to reduce air infiltration and insulates to control heating and cooling losses. It also can be used as a seamless low-slope or flat roofing product on some buildings.

Specifying SPF
Like many other versatile building products, different types of SPF meet different needs. Three general types of field-applied SPF are available:
  • low-density, open-cell SPF;
  • medium-density, closed-cell SPF; and 
  • high-density, closed-cell SPF.
The classification of open-cell or closed-cell refers to the foam’s cellular structure and the method used to create the micro-bubbles that allow SPF to insulate so well. Open-cell SPF uses water as the blowing agent. The water quickly reacts with other chemicals in the mixture to produce carbon dioxide (CO2), which expands the polymer cells. Once expanded, the CO2 leaves the cells and is replaced by air, leaving behind a layer of semi-rigid foam.

Closed-cell SPF uses a chemical blowing agent, which is retained inside the polymer cells after the foam is formed. This creates a rigid, dense foam.

Low-density, open-cell SPF (also called half-pound SPF) is a soft, semi-rigid foam that is effective at insulating and air sealing spaces with unusual angles. This type of SPF often is used in an unvented attic assembly, in a vented attic’s ceilings and in rim or band joists, as well as in walls for both thermal and sound control.

Medium-density, closed-cell SPF can be used for applications typical of low-density, open-cell foam, and to insulate concrete below-grade slabs or foundations and places where space is limited and a higher R-value per inch is required. As a rigid foam, medium-density SPF has been shown to improve wind uplift performance for roofs in high wind climates and racking strength for homes and buildings.

High-density, closed-cell SPF is an ideal roofing material for low-slope roofs in residential, commercial or institutional buildings. Its higher compressive strength and seamless application helps create a waterproof surface well-suited for industrial roofing applications.

Energy-Efficient Attributes
One of the biggest benefits of SPF insulation is its ability to serve as both insulation and an air barrier. SPF’s high performance can be seen in its R-values. Half-pound SPF typically has an R-value of R-3.5 to R-4.5 per inch of thickness. Because this type of foam is light and flexible and easily expands into the nooks and crannies of a building envelope, it provides an ideal barrier to air leakage and superior noise suppression.

The R-values for medium-density foam typically fall between R-6 and R-7 per inch of thickness. At a thickness of about 1.5 inches or more, this type of SPF can serve as a vapor retarder and help control water vapor diffusion.
Additionally, closed-cell SPF can help increase a building’s strength and water resistance. When applied to the interior side of the roof on a home, this type of SPF can provide greater resistance to wind uplift.

Safety and Quality Considerations
During application and curing, it is important to establish a work zone that is clear of other trades and building occupants. After SPF has been properly mixed, applied and cured, it is considered a relatively inert material.

SPF must be installed by a professional contractor and handled according to the manufacturer’s recommendations. The Spray Polyurethane Foam Alliance (SPFA) offers a Professional Certification Program for insulation and roofing applicators. SPFA’s program is operated in compliance with the internationally recognized ISO-17024 standard.  

Jim Perkins is president of SWD Urethane and vice chair of the
 Spray Foam Coalition for the American Chemistry Council’s
 Center for the Polyurethanes Industry. For more information, visit