Foam Board Insulations: Plagued By Ozone, Global Warming and Fire

Tom Lent - May 20, 2010

Foam board insulation presents one of the tougher challenges for green building. With excellent performance characteristics and high R values - from 4 to 5 per inch or beyond - foam boards have been very popular for insulating foundations, walls and roofs in high performance designs. As we’ve reviewed the chemistry of these foams for the Pharos Project, however, we’ve learned that the chemistry that goes into making the most popular foams - polyisocyanate, such as Thermax, expanded polystyrene (EPS) such as Falcon Foam and extruded polystyrene (XPS) such as Styrofoam - is highly problematic for human health and the environment.

The manufacturing processes for both polyisocyanate and polystyrene are based upon highly toxic chemicals that receive red flags in Pharos as materials of very high concern. The toluene diisocyanate (TDI) building block for polyisocyanate is a known carcinogen and the styrene component of polystyrene is connected with a range of hazards from asthma to endocrine disruption, neurotoxicity and cancer. That, however, is just the beginning of the problems.

These plastics work their thermal magic thanks to the foaming process that creates countless tiny insulating pockets in the board. The CFC (chlorofluorocarbon) chemicals originally used to do this foaming were among the most potent ozone destroying chemicals. The Montreal Protocol, the international agreement to protect the earth’s ozone layer, has slowly forced the industry to phase out the worst ozone depleting agents and find alternatives. Some manufacturers are converting to HFCs (hydrofluorocarbons) while others are finally getting away from halogenated compounds entirely, converting to pentane-based foaming agents with little or no ozone destructive potential.

Avoiding damage to the ozone layer, however, has come at a cost. Some of these blowing agents, such as the HFC-134A used in Styrofoam are even more potent global warming gases than the CFCs they replaced, leading to serious questions about the basic efficacy of this insulation to fight global warming, an issue that warrants further attention. Furthermore, the hydrocarbon blowing agents being used instead of the HCFCs are adding to the flammability of these plastics. While manufacturers rarely disclose their fire retardant on a product’s Material Safety and Data Sheet (the MSDS), our research indicates that halogenated fire retardants are used in virtually all US production - usually TCPP (tris(chloropropyl) phosphate) in polyisocyanates and HBCD (hexabromocyclododecane) in the polystyrenes.

The HBCD fire retardant in polystyrenes is now the target of high concern globally. This persistent, bioaccumulative, and toxic chemical is associated with hormone disruption and reproductive disorders and is one of the top sixteen chemicals being studied for elimination on the European Commission’s “Substances of Very High Concern" list. According to the Green Science Policy Institute (GSP), “It has been widely detected in household dust, sewage sludge, breast milk and body fluids as well as wildlife and the global environment. HBCD is also used with fabrics and plastic; however 85% is used with polystyrene insulation, which is likely the primary source of the global contamination.”

The TCPP in polyisocyanates is not yet as well studied as HBCD, but indications are that it may not be any better. This neurotoxic chemical is a close relative of tris, the carcinogenic compound that was banned as a fire retardant in baby pajamas in the late 70s. 

So what is a green designer or builder to do?

* Speak up and push for disclosure - Let your foam insulation sales reps know that you don’t like the choices currently available on the market, and push them to disclose what they are using and explore alternatives. European firms are beginning to employ safer non-halogenated fire retardants like triethyl phosphate (TEP).

* Ask for versions without fire retardants for below grade - As Environmental Building News noted in an excellent article on the topic, a significant percentage of insulation applications are below grade and hence have zero fire risk and have no need for retardants. Ask your insulation reps to provide a well-marked retardant-free option for these applications.

* Avoid the toxic foam boards entirely - Use a blanket or batt insulation that does not require halogenated flame retardants where possible. Where a board insulation is needed, check out the fiberglass and mineral fiber-based boards. We’ll discuss the options for formaldehyde-free binders and bio-based fibers in these blankets and boards as well as aerogel technology in blogs in the near future.

Some very creative alternatives are on the horizon, including Ecovative Design’s board made from agricultural byproducts woven together by the mycelium roots of mushrooms. Sounds implausible, but they’ve already demonstrated a class 1 fire rating and passed a battery of ASTM tests for mold growth, water sorption, and vapor transmission. It’s only available as a packaging material this year, but we’ll be watching them and rooting for their success.