In addition, new blowing agents are in development, with several chemical companies expected to introduce fourth-generation blowing agents within the next two to three years, with zero ozone depletion characteristics and a radically improved climate change profile of less than 15 GWP, according to Duncan. The EBN article acknowledges that this would change the equation.

Recycling polyurethane foam presents another challenge. As a thermoset material, it cannot be melted or broken down into its components for reuse. This means that even jobsite waste is hard to recycle, so proper installation with minimum overspray is essential to achieve environmental efficiency. Foam can be shredded and used as packing material or filler, but given that foam sticks to building structures and is difficult to extract and separate from other materials during demolition, the labor, transportation, and processing costs required for reuse are not usually justified.

Toxic Blowing Agents and Fire Proofing

Fully cured polyurethane foam contains no residual off-gassing. Nevertheless, foam insulation contains hazardous chemicals such as benzene and toluene, which pose a potential hazard concern during manufacture, transport, and installation. This is why installers must be trained and wear protective gear—a portion of the blowing agents in closed-cell foam dissipate during installation, releasing VOCs and greenhouse gases during application.

Manufacturers no longer use polybrominated diphenylethers (PBDEs), synthetic fire-resistance chemicals that pose grave health and environmental risks, but concerns remain with their replacement. Many manufacturers now use halogenated retardants that pose a health risk to installers and occupants if the foam burns. Safer chemicals exist, such as triethyl phosphate (TEP), a non-halogenated fire retardant, and some manufacturers are moving in this direction.

Regardless of its petroleum makeup and toxicity during application, foam products provide such compelling durability, air infiltration, moisture management, and energy-saving advantages that their use continues to grow. Manufacturers are working to keep improving their products from an environmental perspective, including a new generation of high-density open-cell, water-blown foam.

Cost remains the most significant market barrier to more prevalent use of foam in the building industry at large, but some contractors have found ways to obtain the advantages of foam while shaving off some of the increased cost. For example, some builders use a hybrid insulation system called “flash and batt,” applying 1 to 2 inches of closed-cell spray foam to a wall cavity first followed by a standard fiberglass batt, cellulose, or, in some cases, even open-cell foam. This provides the air-sealing benefits, with improved R-value, at lower cost. Some builders use foam only in difficult-to-insulate areas, such as rim joists and eaves, where even the best installers have trouble matching the air seal and vapor-retardant qualities of foam.

Fernando Pagés Ruiz develops ecologically minded affordable housing in the Midwest and mountain states. His two books, Building an Affordable House and Affordable Remodel, are available from The Taunton Press.