When we were updating the insulation in our 100-year-old house in 2002, a spray foam product called Icynene was recommended to us as the best way to transform our uninsulated attic space into the surest protection against Minnesota’s frigid winters. Men dressed head to toe in white suits and donning breathing apparatus sprayed expanding foam in what would become a finished attic. There’s a good reason they wore all that protective gear: the chemicals in polyurethane foams like Icynene are known to be hazardous to human health. No one involved in the project thought to mention that perhaps we the homeowners should likewise be concerned about air quality during or after installation.

Thankfully, we suffered no noticeable ill effects after having spray foam installed in what’s now a master bedroom, though we’ll probably never know for sure if it has longer-term impacts on our health. Not all homeowners have been so lucky. As more buildings have been insulated with spray foam (over 350,000 with Icynene alone, and there are numerous brands on the market), reports of respiratory and neurological reactions have mounted, many serious enough to require occupants to move. Several class-action lawsuits claim that “severe health issues” stemmed from installation of spray foam in plaintiffs’ houses.

Concern about Spray-Foam Compounds

The process of applying spray foam insulation involves a chemical reaction between two liquid compounds. In the case of “open-cell” foams, the ingredient known as the “blowing agent” is simply water. “Closed-cell” foams generally rely on hydrofluorocarbons, the human health effects of which are not completely understood. Most spray foams contain isocyanates, known to be “powerful irritants to the mucous membranes of the eyes and gastrointestinal and respiratory tracts” that can cause long-term sensitization, according to The National Institute for Occupational Safety and Health (NIOSH).

Other components of spray foam include polyols, flame-retardants and amines, as well as some proprietary ingredients that manufacturers do not disclose. The EPA reports that “during and after installation [these chemicals] can cause asthma, sensitization, lung damage, other respiratory and breathing problems, and skin and eye irritation.” Some exposed to spray foam have become so sensitized to the compounds that they react any time they enter a building insulated with spray foam. Many flame-retardant chemicals are also suspected endocrine disruptors and possible carcinogens. Not sounding too green, impressive insulating abilities notwithstanding.

Manufacturers claim that in laboratory testing, once the insulation dries it becomes inert and should not pose a risk to human health. In practice, however, imperfect installation can mean that unreacted (and therefore still dangerous) chemicals linger, causing respiratory and other problems for the unhappy occupants of these buildings. The compounds are also a concern in the dust created when the product is trimmed.

Environmental health experts have questioned the assumption of spray foam’s safety and believe more research is necessary to prove that it isn’t hazardous to human health. Even the EPA has noted that “The potential for off-gassing of volatile chemicals from spray polyurethane foam is not fully understood and is an area where more research is needed.”

If you’re generally a proponent of the precautionary principle, you might seek out alternative insulations until independent studies prove spray foam’s safety conclusively or manufacturers come up with more benign formulations.

Other Issues with Spray Foam

There are some other serious concerns about spray foam. In addition to the poor performance that can result from improper installation (a risk with just about any insulation product), spray foam is really tough to remove. If you decide you want to insulate with something else or you’re one of the unlucky folk with imperfect installs, you’re pretty much stuck, like the insulation is to your walls. Remember, spray foam expands to fill every crevice, so you can’t just pull it out like a fiberglass batt. It’s also incredibly sticky. We had to use carbide scrapers to remove it from wood where the installers weren’t careful enough with drop cloths. The difficulty of removal also affects the ability to recycle materials when remodeling or demolishing a building.

Of far greater concern are the chemicals emitted if spray foam burns in a fire. Though full of flame retardants, if sprayed-in foam does catch fire, the fumes are highly toxic. There have even been a few cases where improper installations have caused fires.

The Climate Impact of Spray Foam: More Harm than Good?

The other core issue to consider with spray foams is the greenhouse gas emissions associated with their use. Many of us beef up the insulation in our homes in order to reduce the climate impact of energy use. It turns out that some spray-foam insulations, though very effective at slowing heat movement, use compounds with such potent global warming effects that they essentially undo the climate benefits of saving energy.

Closed-cell foam is far more dense and is therefore a more effective insulator than open-cell foam, but the compounds used in blowing agents for most closed-cell foams have extraordinarily high global warming potential (GWP). Alex Wilson, executive editor of Environmental Building News, reports that the blowing agents used in most closed-cell spray foams have global warming potential over a thousand times greater than carbon dioxide. He estimates that if 50 percent of these agents escape over time, the “payback” for the greenhouse gas emissions of four inches of insulation would require up to a century of energy savings.

Some newer entrants into the spray-foam market may have found ways to reduce the high-GWP of the hydrofluorocarbons usually used in closed-cell foam. Open-cell foams usually use water as a blowing agent and therefore have lower GWP, but they’re not as effective insulators. Their R-value is low enough that it’s worth considering other forms of insulation that are better understood in terms of their impact on human health.

Some newer spray foams also incorporate soy or other plant-based materials, at least in part. The amounts of bio-based components in most spray foams advertised as such are apparently so small that many in the industry see them simply as examples of greenwashing.

Many in the green building field now steer consumers away from foam when possible, towards products considered only somewhat less effective at insulating, the health effects of which are currently considered less risky.

But some in the industry believe that foam still has a place as we seek to make our buildings more efficient. Senior editor of Green Building Advisor and self-described “energy nerd” Martin Holladay thinks that “spray foam insulation is a useful building product that has many applications.” He notes that “most weatherization contractors engaged in air sealing work would be hard pressed to do their jobs if they couldn’t use spray foam insulation for certain applications. … There are some air leaks in older houses that can only be sealed with spray foam. Reducing air leakage with spray foam can reduce the amount of fuel needed to heat a house in a cold climate, and that type of energy savings can be one way to address climate change.”

In the last decade consumers have gotten more skeptical of the safety promises made by manufacturers of a wide range of products. Fewer of us are willing to blindly accept that products sold to us as safe in fact are, and we’re asking more informed questions. The 2002 spray foam in our attic is there to stay. But we’re now looking to reinsulate our rim joists (those pockets in the basement where the house meets the foundation), and all the contractors we’ve spoken to say spray foam is the only kind of insulation worth considering for an area prone to moisture. You can bet I’m looking carefully into alternatives.

If you’re a homeowner wishing to make your home more efficient without potentially compromising your health, you have options besides spray foam, though they will vary greatly depending on what you’re trying to accomplish. Check out the follow-up to this piece, “Beyond R-Value: The Complex Calculus of Choosing Insulation,” for help sifting through the far-from-straightforward decisions you face in creating an energy-efficient and healthy home.