For decades, rigid foam insulation was manufactured using chlorofluorocarbons (CFCs) — the same chemicals implicated in stratospheric ozone depletion. The industry has since undergone a series of transitions to less harmful blowing agents, driven by scientific consensus, international treaties, and environmental regulations. Understanding this evolution helps builders make informed choices
Chlorofluorocarbons (CFCs) are stable, non-toxic, non-flammable chemicals that were widely used as refrigerants, aerosol propellants, and foam-blowing agents throughout the 20th century. Their stability is precisely what makes them dangerous — they do not break down in the lower atmosphere. Instead, they drift slowly upward to the stratosphere, where UV radiation breaks them apart, releasing chlorine atoms that catalytically destroy ozone molecules.
drift slowly upward to the stratosphere, where UV radiation breaks them apart, releasing chlorine atoms that catalytically destroy ozone molecules.
A single chlorine atom can destroy up to 100,000 ozone molecules before it is removed from the stratosphere. The discovery of the Antarctic ozone hole in 1985 led to the Montreal Protocol (1987), an international treaty that phased out CFC production globally.
Blowing Agent
Ozone Depletion Potential (ODP)
Global Warming Potential (GWP)
Status
CFC-11
1.0 (baseline)
4,750
Banned (1996)
CFC-12
1.0
10,900
Banned (1996)
HCFC-141b
0.11
725
Phase-out complete (2020)
HCFC-142b
0.07
2,310
Phase-out complete (2020)
HFC-245fa
0
1,030
Being phased down
HFC-365mfc
0
794
Being p
Rigid foam insulation achieves its high R-value through the use of blowing agents — gases that expand the plastic into a foam structure containing millions of tiny closed cells. The gas trapped inside these cells provides the insulating value. Different plastics and blowing agents produce different R-values:
ing agents — gases that expand the plastic into a foam structure containing millions of tiny closed cells. The gas trapped inside these cells provides the insulating value. Different plastics and blowing agents produce different R-values:
Insulation Type
Traditional R-value (per inch)
Current R-value (per inch)
Blowing Agent Evolution
Extruded Polystyrene (XPS)
R-5.0
R-5.0
CFC-12 → HCFC-142b → HFC-134a → HFO
Polyisocyanurate (ISO)
R-7.0–8.
By 1990, most XPS manufacturers had switched from CFC-12 to HCFC-142b (hydrochlorofluorocarbon). Similarly, polyisocyanurate (ISO) manufacturers transitioned from CFC-11 to HCFC-141b by mid-1993. These HCFCs were significant improvements — they have approximately 5% to 11% of the ozone depletion potential of their CFC predecessors.
Transition to HCFCs
By 1990, most XPS manufacturers had switched from CFC-12 to HCFC-142b (hydrochlorofluorocarbon). Similarly, polyisocyanurate (ISO) manufacturers transitioned from CFC-11 to HCFC-141b by mid-1993. These HCFCs were significant improvements — they have approximately 5% to 11% of the ozone depletion potential of their CFC predecessors.
However, the switch came with a thermal performance penalty. ISO foam produced with HCFC-141b provided R-values that were 6% to 11% lower than foams made with CFC-11. XPS made with HCFC-142b also had lower aged R-values but still met the R-5 per inch specification of its CFC predecessors. The environmental gain came at the cost of slightly thicker insulation for the same thermal performance.
The Next Phase: HFCs and the Kigali Amendment
HCFCs were always intended as transitional blowing agents. Under the Copenhagen Amendment to the Montreal Protocol, developed countries were required to phase out HCFCs entirely by 2020. The replacement — hydrofluorocarbons (HFCs) — have zero ozone depletion potential but high global warming potential (GWP).
The Kigali Amendment (2016) to the Montreal Protocol addressed this by phasing down HFCs. For the foam industry, this means transitioning to hydrofluoroolefins (HFOs) and hydrocarbons (pentane, isopentane, cyclopentane), which have near-zero ODP and very low GWP.
Current State of the Industry
Polyisocyanurate (ISO)
Most ISO manufacturers in North America and Europe have now transitioned to pentane-based blowing agents or HFO blends. These materials achieve aged R-values of R-5.6 to R-6.5 per inch — somewhat lower than the best CFC-era numbers but with an environmental cost measured in single-digit GWP. Pentane-blown ISO is now the standard for commercial roofing insulation.
Extruded Polystyrene (XPS)
XPS manufacturers have transitioned through several chemistries. The latest generation uses HFOs with GWPs below 10, compared to the 2,310 GWP of HCFC-142b. Some manufacturers now offer XPS with a “near-zero” GWP label. The R-value remains at R-5.0 per inch.
Spray Polyurethane Foam (SPF)
Spray foam has followed a similar path. Closed-cell SPF now uses HFO blowing agents with GWP as low as 1. The R-value of closed-cell SPF has declined slightly from the CFC-era peak of about R-7.0 per inch to about R-6.0 per inch, but the environmental benefit is substantial.
Expanded Polystyrene (EPS)
EPS has always been the environmental standout among rigid foams. It uses pentane as a blowing agent, which dissipates from the foam within weeks after manufacturing. The cells are then filled with air, providing consistent R-3.8 to R-4.2 per inch throughout the product’s lifetime. EPS has zero ODP, near-zero GWP, and contains no halogenated chemicals.
Phenolic Foam: A Historical Note
Phenolic foam was once manufactured in the United States with CFC-11 blowing agents. These foams had excellent fire resistance and high R-values. However, phenolic foams are no longer produced in the U.S. due to manufacturing complexity and market competition from ISO and SPF. In Canada, two manufacturers continue phenolic foam production using safer blowing agents.
Practical Guidance for Builders
Choosing Insulation for Environmental Performance
EPS is the most environmentally friendly rigid foam, with zero ODP and near-zero GWP. Use it for below-grade, above-grade, and roofing applications where R-4.0 per inch is adequate.
ISO with pentane or HFO blowing agents offers the highest R-value per inch among environmentally responsible options. Best for applications where space is limited.
XPS with HFO blowing agents provides good compressive strength and water resistance for below-grade applications, with much-improved environmental profile.
Rigid fiberglass and mineral wool boards are alternatives for applications requiring non-combustible insulation. They use no blowing agents and have no ODP or GWP concerns.
Avoiding Trade-offs with Energy Efficiency
In the pursuit of environmentally friendly insulation, it’s important not to sacrifice energy efficiency, which also has a major environmental impact through reduced heating and cooling energy use. If you choose a lower-R-value insulation due to environmental concerns, compensate with greater insulation thickness to maintain the same overall thermal performance.
The rigid foam insulation industry has undergone a remarkable transformation over three decades, moving from CFCs to HCFCs to HFCs and finally to HFOs and hydrocarbons — each step dramatically reducing environmental impact. For today’s builder, the choice is no longer between performance and environment. Modern foam insulations using pentane, HFO, or CO₂ blowing agents provide excellent thermal performance with negligible ozone depletion impact and very low global warming potential. By understanding the chemistry behind insulation, builders can make choices that serve both their clients and the planet.
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