Insulating and air sealing are effective ways to reduce the carbon footprints of homes and other buildings, and rigid foam panels are a popular material for doing that work. But many of the panels have a little-known climate cost: the global warming potential (GWP) of the gas, or blowing agent, used to puff the foam.
In the case of panels made of extruded polystyrene (XPS)—a closed-cell foam suitable for wet or dry conditions—that gas has been hydrofluorocarbon-134a (HFC-134a). HFC-134a is a good blowing agent, but it has a GWP of 1,430, meaning it traps 1,430 times as much heat as carbon dioxide does over 100 years. As regulations seeking to eliminate HFC-134a take effect this year in Canada and the US, panel makers including Owens Corning and DuPont are switching their blowing agents to blends containing hydrofluoroolefins (HFOs).
Refrigeration is the largest use for HFCs and other fluorocarbon gases, using around 45% of the supply in North America; blowing agents use roughly 9%, according to the market research firm IHS Markit. The same key feature—a phase transition from liquid to gas at near-ambient temperatures—makes them useful in both cooling and foam manufacturing.
But cooling is done in closed-loop systems that leak a few percent a year or less. “The main thing about foams and why we even care about them is because they leak, and we can’t really recover it,” says Christina Theodoridi, a technical analyst at the Natural Resources Defense Council, an environmental group. “Once it goes into the product, it’s out into the atmosphere.” In addition to what’s trapped in the final product, the blowing agent is also emitted during the blowing process itself.
HFCs weren’t always sustainability villains. The chemical industry introduced HFCs in the 1990s to replace hydrochlorofluorocarbons (HCFCs), which deplete the ozone layer and have high GWPs. In the 1980s, HCFCs replaced chlorofluorocarbons (CFCs), which were worse on both measures. HFCs have minimal effect on the ozone layer but are potent greenhouse gases with lifetimes of around 14 years in the atmosphere.
Honeywell, Chemours, and other fluorochemical makers—the same companies that made CFCs and HCFCs—developed HFOs in the first 2 decades of the 2000s. HFOs have a negligible effect on the ozone layer and GWPs near 1, according to José Méndez-Andino, chief R&D officer at Owens Corning. Before taking on that role earlier this year, Méndez-Andino led R&D for the firm’s insulation and roofing business.
The main reason for the low GWP, he says, is that unlike their predecessors, HFOs contain a double bond. Up in the atmosphere, hydroxyl and other radical species can react with that double bond, degrading the HFOs in 20–40 days.
One factor complicating this chemical switchover is that the new blowing agents blend HFOs with things like pentane, whereas HFC-134a is used all by itself. The main reason for blending is the higher cost of HFOs, says Rajiv Banavali, who was the chief technology officer for the advanced materials group at Honeywell while the firm was developing HFOs.
Banavali says that HFO-1233zd—technically a hydrochlorofluoroolefin because it contains one chlorine—is the leading blowing agent blend component, followed by HFO-1234ze and HFO-1336mzz(Z). The refrigeration industry is rapidly adopting HFO-1234yf, especially for automotive air-conditioning. In addition to having lower GWPs, HFOs are better insulators than HFC-134a, Banavali says.
But replacing HFCs is not simple, says Jeff Hansbro, DuPont’s global advocacy director. In addition to low cost and low GWP, the firm looked for low thermal conductivity and permeability, high vapor pressure, and sufficient solubility in polystyrene to create a uniform cellular structure in the finished foam. Finding that balance meant testing numerous substances and blends, Hansbro says. Among single-component HFO blowing agents, he adds, “none of them have proven to be singular drop-in solutions capable of meeting all the performance metrics.”
Blowing agents can even interact with the dyes in the foam, Méndez-Andino says. Owens Corning’s XPS boards are branded with the Pink Panther character, and the company wanted to keep the color consistent. “Our customers expect us to be pink,” he says. The firm is calling its pink, low-GWP foam Foamular NGX and pointing out its regulatory compliance on the label.
DuPont is taking the opposite tack, changing the color of its Styrofoam-brand XPS boards from blue to gray and highlighting the switch with a marketing campaign called Beyond Blue.
Though retailers have a lot of discretion on price, the low-GWP XPS foam boards are currently around 15% more expensive than HFC-blown boards at hardware stores. Banavali says HFOs are inherently more expensive to produce than HFCs, but he expects that gap to narrow in the coming years for three reasons.
First, economies of scale will bring price down as Honeywell, Chemours, Arkema, and others make HFOs in larger and larger volumes to meet growing demand in foam, refrigeration, and other uses. Second, many of the core production and handling technologies will lose patent protection soon. And third, regulations like the ones coming into effect in North America will change the market, Banavali says.
On a global scale, an international agreement called the Kigali Amendment drives the phaseout of HFCs, according to the NRDC’s Theodoridi. It builds on the Montreal Protocol, which mandated the elimination of CFCs. The US is party to the Montreal Protocol but has not yet joined the Kigali Amendment, though in January, President Joe Biden directed the US Department of State to submit it to the Senate for ratification. Theodoridi expects it to pass with a bipartisan majority, much like a provision last year that gave the US Environmental Protection Agency the authority it would need to enforce federal regulations.
In the meantime, California, Colorado, New Jersey, New York, Vermont, and Washington have state-level bans on HFC-134a as an XPS-blowing agent as of Jan. 1. Maryland and Massachusetts will join that list July 1, and Hawaii, Maine, Virginia, and Rhode Island are looking at Jan. 1, 2022, to enact their versions. Canada took a broader approach, banning any blowing agent or blend with a GWP higher than 150.
Owens Corning’s NGX line is on the market in areas with enacted regulations. DuPont has gray, HFC-134a-free XPS panels out as well, though it is still finalizing its formulation and building code approvals. Both firms tell C&EN they expect to convert all their North American XPS lines to HFO blends over the next few years.
In total, about 80 million m2 of XPS panels are sold in North America each year, Owens Corning says, representing about a quarter of the insulation panel market.
The shift from HFCs to HFOs could have a big climate impact. Blowing XPS consumed 10,000 metric tons (t) of fluorocarbons in North America in 2020, according to IHS Markit. A 2018 United Nations report concluded that eliminating HFC-134a as a foam-blowing agent worldwide would avoid the equivalent of more than 1 billion t of CO2 emissions.
XPS makers are technologically ready to switch to HFOs, Theodoridi says, so they should lock in their supplies now before other HFC users start clamoring for them. “It’s pretty clear where the whole world, not just the US, has to go,” she says. “And the faster industry reduces its reliance on HFCs, the better equipped they are for what’s coming.”