Next-gen sprayfoam systems: shifting to HFO blowing agents

by arslan_ahmed | September 19, 2022 7:00 am

By Doug Brady

Photos courtesy Huntsman Building Solutions

Spray polyurethane foam (SPF) is a building material commonly used in both insulation and roofing applications. The material is manufactured in three core densities, which correspond to the material’s application, or use. The first is open cell insulation, commonly offered at 8-kg/m3 (0.5-lb/cf) density, the second is closed cell insulation, commonly offered at 32-kg/m3 (2-lb/cf) density, and the third is roofing spf, commonly sourced at 40- to 56-kg/m3 (2.5- to 3.5-lb/cf) density. The sprayfoam industry is currently leading an important effort which directly impacts closed cell SPF insulation and roofing SPF. This initiative is a shift away from the use of hydrofluorocarbons (HFC)-based blowing agents to the use of hydrofluoroolefins (HFOs)-based blowing agents.

HFCs[2] are any of several organic compounds composed of hydrogen, fluorine, and carbon, while HFOs are unsaturated organic compounds composed of hydrogen, fluorine, and carbon. Unlike traditional HFCs and their blowing agent predecessors, clorofluorocarbons (CFCs), both of which are saturated, HFOs[3] are olefins, otherwise known as alkenes.

The push toward HFO-based sprayfoam blowing agent technology is the latest step in an ongoing evolution to phase out the use of chemicals known to harm the ozone and climate. In addition to reducing the negative Earth impacts of sprayfoam insulation and roofing materials, there are also product performance and installation considerations. This article will explain the blowing agent shift and why it matters to those considering the specification of sprayfoam for both insulation and roofing applications in commercial building projects.

Blowing agents explained

The Handbook of Foaming and Blowing Agents defines a blowing agent as a substance capable of producing a cellular structure via a foaming process in a material that undergoes hardening or phase transition. Examples of such materials are polymers, plastics, and metals. Two types of blowing agents are distinguished—chemical and physical. Above a certain temperature, or in contact with another specific chemical, it will initiate a chemical reaction that generates a gas. At the same time, a solid plastic is made.  The formation of a plastic and the generation of a gas (chemical and/or physical) at the same time make a solid foam structure. Physical blowing agents are metered into the plastics, most frequently in the form of a melt, and they form bubbles by various means.

Blowing agents further divide into endothermic and exothermic foaming agents. Endothermic chemical foaming agents take heat away from the chemical reaction, producing foams with a much smaller cell structure, resulting in improved appearance and better physical properties. Exothermic chemical foaming agents generate heat during the decomposition process. They liberate more gas per gram of foaming agent than endothermic agents and produce higher gas pressure.1

Usually, exothermic blowing agents tend to make larger cells compared to endothermic. In a system, a good balance between endothermic and exothermic blowing agents will make a better dimensionally stable foam. As a further rule of thumb, endothermic blowing agent gives higher R value to the foam.

HFC- and HFO-based, sprayfoam blowing agents are both physical, endothermic blowing agents.

The European FluoroCarbons Technical Committee (EFCTC), a Cefic Sector Group, further defines what makes a good insulation foam blowing agent, stating the “foam blowing agent is selected to provide a closed-cell structure which minimizes heat transfer, in part due to the properties of the foam blowing agent, which is retained within the foam essentially for the lifetime of the foam’s use.”

Professional sprayfoam contractor installs closed cell sprayfoam as continuous insulation (ci) application

Producers dissolve the blowing agent into foam precursors where it expands to form the foam once injected or sprayed, causing the foaming reaction to begin. Optimization is crucial to ensure thermal efficiency and overall performance. Foam blowing agents with low thermal conductivity can improve insulation properties of the foam, allowing better insulation performance or thinner profiles for the same insulation value. The committee further points out how emissions of the foam blowing agent[5] from closed cell foam are typically less than two percent annually, so this thermal performance persists over time.

 The evolution of blowing agents

Blowing agents used in SPFs have evolved over time, with the phase out of specific compounds occurring at various points  in the past. The first class of blowing agents used in sprayfoam were chlorofluorocarbons (CFCs). They have a global warming potential (GWP) of more than 4000 and an ozone depletion potential (ODP) of one. Second generation blowing agents
were hydrochlorofluorocarbons (HCFCs), which have a GWP
of more than 725 (and can range up to 2310) and an ODP of approximately 0.055 to 0.11[6]. The U.S. government banned CFCs in 1996 because of their ability to degrade the Earth’s ozone layer. It later banned HCFCs in 2005 for the same reason.

HFCs are the third iteration of sprayfoam blowing agents and are still in use today. They offer zero ODP; however, have a GWP value[7] of more than 794 (and up to 3220). Once considered a suitable replacement for ozone-depleting substances, HFCs are now the world’s fastest-growing greenhouse gases. HFCs have up to 4000 times more global warming impact[8] than carbon dioxide (CO2). Scientists estimate HFCs alone could contribute up to 0.5 C (32.9 F)[9] of global warming by the end of the century.

It is for this reason the industry is shifting towards the use of HFOs[10], which offer zero ODP and a GWP value of less than 25. Pending the blowing agent in question, some HFOs offer a GWP value of one. Note the dramatic difference in GWP between first generation blowing agents (CFCs) and the new, fourth generation of blowing agents (HFOs)—an initial GWP of over 4,000 to a GWP of just 1 today.

A defining moment: 1987’s Montreal Protocol

An international effort to protect the Earth is the backdrop for the periodic phase out of specific sprayfoam blowing agents. This effort began as an effort to slow the loss of stratospheric ozone when, in 1987, the international community signed the original Montreal Protocol. The agreement mandated that developed countries begin phasing out the use of Chlorofluorocarbons (CFCs), which are known to destroy the Earth’s ozone layer. This agreement called for participating countries to achieve a 50 percent reduction in the use of CFCs relative to 1986 levels by 1998. The Montreal Protocol was essentially the world’s first step of many in protecting the ozone layer.

However, after this international treaty was signed, new data became available that demonstrated worse than expected ozone layer damage. This data ultimately led to a series of amendments to the initial agreement, all of which were aimed at controlling additional ozone depleting chemicals[11] and identifying mechanisms to enforce the compliance of developing countries. The amendments, in sequential order, include the London Amendment in 1990, the Copenhagen Amendment in 1992, the Montreal Amendment in 1997, the Beijing Amendment
in 1999, and the Kigali Amendment in 2016.

The latter amendment is notable as its goal was to phase down the production and use of HFCs. It aimed to address the fact the use of HFCs results in greenhouse gases known to be incredibly detrimental to the Earth’s climate. At the time of the amendment’s ratification, U.S. President Barack Obama and his administration strongly supported the effort.

Installer in personal protective equipment (PPE) suit applying hydrofluoroolefin (HFO)-based sprayfoam.

U.S. support for the Montreal Protocol stalled however under the Trump administration, which removed the United States from the Paris Climate Agreement, blocking HFC phasedown efforts. Subsequently, when Biden took the helm in January 2021, one of his first actions as President was to return the country to the Paris Agreement, officially signaling the country’s return to focus on the curbing of greenhouse gases as well as policies aimed at reversing climate change.

In addition to direct impacts on the environment, all this federal and international history directly impacts the commercial building, insulation, and roofing sectors, as all use various closed cell sprayfoam solutions. Most notably however, and irrespective of U.S. sentiment or policy at the federal level at any given time, top industry leaders have been working to move the construction industry toward adopting next generation sprayfoam systems incorporating HFO-based blowing agents known to reduce global warming inducing greenhouse gases. Individual states have also started taking phasedown initiatives into their own hands.

State-by-state phasedown efforts

Established under the Clean Air Act (CAA), the Environmental Protection Agency’s (EPA’s) Significant New Alternatives Policy (SNAP) program identifies and evaluates substitutes for ozone-depleting substances by end-use. SNAP Rules 20 and 21 list specific HFCs as unacceptable and call for the shift to environmentally friendly refrigerants and blowing agents. However, SNAP rules were vacated at the federal level in 2017, after the Mexichem Fluor Inc. v. EPA lawsuit claimed the EPA had exceeded its statutory authority. In 2020, SNAP rules were partially reinstated and currently prohibit certain substitutes when switching from ozone-depleting substances. However, in response to the partially vacated rules in 2017, member states of the U.S. Climate Alliance, a coalition of states[13] committed to upholding the Paris Climate Agreement’s goal of keeping temperature increases below 1.5 C (34.7 F), began to adopt SNAP Rules 20 and 21 at the state level and this effort continues today.

Participating states are in various degrees of HFC phasedown. In addition to enacting legislation prohibiting certain HFCs, U.S. Climate Alliance member states California and Washington have gone beyond, and enacted stricter regulations aimed at curbing HFC emissions beyond EPA SNAP Rules 20 and 21. Additionally, Colorado, New York, Maine, Vermont, New Jersey, Delaware, Rhode Island, Maryland, and Massachusetts are all U.S. Climate Alliance members who have enacted legislation prohibiting certain HFCs in alignment with the federal SNAP 20 and 21 rules. Pennsylvania, Connecticut, Oregon, New Mexico, and Hawaii are members which have expressed intentions to introduce legislation to reduce HFC emissions, but no bills have yet been signed into law in these states. Finally, Nevada, Minnesota, Wisconsin, Michigan, Illinois, Louisiana, and North Carolina are member states but have not yet committed to regulating HFCs. The remaining states[13] are not U.S. Climate Alliance members.

Regardless of which states participate and which do not, the sprayfoam industry continues to introduce HFO-based, closed cell sprayfoam systems to provide more environmentally sound solutions for optimizing the performance of both the building envelope and roof.

Closed cell sprayfoam insulation

Closed cell spray polyurethane foam acts as a single-source solution for thermal, air, water, and vapor control, providing architects and builders with the ability to seal the building enclosure via one product and eliminating the need to specify numerous additional products. The material is durable, versatile, lightweight, and is a rigid foam option.

Closed cell sprayfoam adheres to nearly every construction substrate, expanding and forming in place, virtually eliminating cracks and gaps that leak air and water in above grade walls. It keeps its shape without settling, creating an airtight structure providing consistent performance over its lifetime.

Next generation sprayfoam using hydrofluoroolefin (HFO)-based blowing agent applied to commercial facility exterior.

As a thermal insulator, closed cell SPF boasts one of the highest R-values per inch of all insulation options available. The material is ideal for continuous insulation (ci) applications in commercial structures and can be used in both interior and exterior applications where it can replace rigid extruded polystyrene (XPS), mineral wool, fiberglass, and polyisocyanurate (PIR) foam boards. The material
boasts low water absorption as well as resistance to mold, as demonstrated with ASTM C1338. Closed cell sprayfoam excels as a water-resistive barrier (WRB) on exterior wall applications and is tested in accordance with ASTM E2357, with a pressure up to 300 Pa (0.04 psi) for air barrier assemblies which included the ASTM E331 (AC71), Water Penetration Testing. The result was no leakage through the sprayfoam.

The air sealing capabilities of closed cell SPF insulation maintain indoor temperatures and reduce energy costs. They also improve indoor air quality (IAQ), minimizing the volume of allergens and pollutants able to enter the structure. Combined, these qualities result in an optimized building envelope, creating greater indoor comfort and reducing long-term heating and cooling demands.

When applied in walls, ceilings, and floors, the Federal Emergency Management Agency (FEMA) names closed cell sprayfoam a Class 5 material, the highest classification for products indicating strong resistant to floodwater damage. Class 5 materials do not require special waterproofing protection, can survive wetting and drying and may be successfully cleaned after a flood to render them free of most harmful pollutants.2 While closed cell sprayfoam may be applied as cavity insulation or as continuous insulation in commercial structures and still qualify as a Class 5 material, it is the only cavity insulation approved by FEMA with this highest floodwater resistance. When applied under slab as insulation, closed cell sprayfoam is also flood and radon resistant.

The application of closed cell SPF in above grade walls can also increase the structural strength of buildings and assist with wind resistance. The degree of hardening depends primarily on the strength of the building. For example, an I-beam modular constructed metal building with a 22-gauge metal panel will benefit significantly less, regarding racking strength, from an interior application of closed cell SPF than a post-frame constructed building with 29-gauge corrugated metal panels. When installed, closed cell SPF essentially glues the assembly together, reduces the potential for movement, and adds a tensile strength average ranging from 103 to 172 kPa (15 to 25 psi).3

The Spray Polyurethane Foam Alliance (SPFA) conducted racking performance tests in 1992 and 1996 and at Architectural Testing Inc. in York, Pennsylvania in 2007. The tests demonstrated that medium density closed cell SPF, installed at 32 kg/m3 (2 lb/cf), increases racking strength by 70 to 200 percent in wall assemblies sheathed with oriented strand board (OSB), plywood, gypsum wallboard, vinyl siding, and polyiso board. The research proved closed cell SPF significantly increased rack and shear strength in both wood and metal construction. Installed SPF also increases the strength of weaker substrates such as gypsum drywall, vinyl siding, and polyiso foam insulation at a much greater percentage than stronger substrates such as OSB and plywood. Notably, special bracing for wind resistance is not required for strengthening purposes when using closed cell sprayfoam in walls.4

Sprayfoam roofing

One of the most rigid of all SPFs, sprayfoam roofing is applied to the top surface of low-slope roofs. In this application, the material acts as both a protective roofing material and as a thermal insulator. Like closed cell sprayfoam insulation, sprayfoam roofing is known for its air sealing capabilities and its energy efficiency. It is also the highest density sprayfoam as it must provide protection from moisture, rain, wind, hail, and other elements, as well as withstand maintenance-related foot traffic. The material offers a compressive strength of 714 to 1071 kg/m (40 to 60 lb/in.).

Sprayfoam roofing is ideal for use when: the roof deck is an unusual shape; the region experiences extreme storms, wind, or hail (coastal and hurricane prone regions are two examples); a sloped application is needed for drainage; the substrate has multiple penetrations (such as with solar panel supports) or there is equipment mounted to the roof requiring flashing; the structure is unable to withstand additional weight on the roof; and when removing the existing roof is deemed too expensive (as sprayfoam roofing may be applied over an existing roof in a cost-effective retrofit application).

Installed on the roof, sprayfoam creates a protective, monolithic layer which serves as continuous thermal insulation layer, WRB, air barrier, and vapor retarder. The material requires an additional coating overtop to protect the surface from ultraviolet (UV) radiation, foot traffic, and any other weather cycling and elements. Acrylic- and silicone-based coatings are two which are more commonly used.

Applied to the underside of a roof, closed cell sprayfoam can increase wind uplift resistance. Applied to built-up roofing and metal substrates, wind uplift resistance is enhanced further. A study conducted by the University of Florida in 2007 found that applying closed cell sprayfoam under a roof deck provides up to three times the resistance to wind uplift for wood roof sheathing panels[15] when compared to a conventionally fastened roof.

SPF roofing is also resistant to progressive peeling failure, which leads to flashings and copings being pulled away from their original locations by wind. Following Hurricane Katrina, the National institute of Standards and Technology (NIST)[16] examined roofs and found buildings with sprayfoam roofs performed well without blow-off of the SPF or damage to flashings.

Since it is closed cell, sprayfoam roofing, like closed cell sprayfoam insulation, is also a Class 5 FEMA flood damage-resistant material. It is impermeable to moisture and may be cleaned and dried.

Manufacturing and performance considerations

When developing sprayfoam systems, manufacturers must be mindful of the inherent established precedents in the market. For instance, the plethora of impingement mix 1:1 ratio in the industry today forces manufacturers of new closed and open cell sprayfoam systems to match this chemical blend. The same may be said for when designing sprayfoam solutions with the next generation of blowing agent.

Compared to HFC, HFO molecules tend to break down faster in resin. Consequently, new catalysts were necessary to pair with the HFO blowing agent to sustain the six-month shelf-life industry expectation. This was one of the most difficult hurdles for sprayfoam manufacturers.

The HFO molecule does have a strong benefit over HFC. Thermal conductivity is lower in HFO than HFC. This translates to better thermal performance, on average, with an HFO-based sprayfoam compared to one that is HFC-based. While the blowing agent is the primary driver of the R-value of a sprayfoam, the overall composition of the resin, in combination with isocyanate, determines the sprayfoam’s R-value. There has been an increase in aged R-values in systems containing HFO blowing agents.

Importance of EPDs and energy modeling

Because of their great thermal resistance and air barrier properties, many buildings use both types of SPF: closed cell (exterior or interior) and open cell (interior). SPF is commonly installed in both residential projects, such as single houses, townhomes/condos, and commercial, as well as institutional and agricultural projects, such as schools, hospitals, arenas, stores, restaurants, storage facilities, data centers, and grow houses.

To reduce the construction and building operations sectors’ contribution to global warming, it is imperative to do two things[17]. The first is to use products that demonstrate reduced embodied carbon. Environmental Product Declarations (EPDs) are important tools for this as they tell the life cycle story of a product in a single, comprehensive report that provides information about a product’s impact on the environment, including global warming potential, smog creation, ozone depletion, and water pollution. While EPDs do not rank products, and the existence of an EPD for a product does not indicate if environmental performance criteria have been met, they are an important disclosure
tool that helps purchasers better understand a product’s sustainable qualities and environmental repercussions, so they can make informed product selections[18].

Secondly, buildings must be constructed tighter, better sealed, and more energy efficient to reduce their operational carbon emissions. To assess performance in this area, energy modeling is useful. The pre-construction, whole-building assessment of energy efficiency uses computer programs for calculation. Designers create a model of the entire building on a computer and run it through simulations to show energy performance, usually for an entire year and based on meteorological information. The modeling[19] accounts for all systems within
a building and examines how they impact each other.


In closing, the sprayfoam industry’s shift to HFO-based blowing agent technology is a crucial step toward reducing the building industry’s global warming contributions. Shifting from third generation HFC-based blowing agents to HFO-based options will evolve the industry from using products with zero ODP and GWP value of more than 794 to the substantially improved newer generations of SPF offering zero ODP and a GWP that can, in certain products, reach a value of one. To be better informed about sprayfoam insulation and roofing system’s individual performance and Earth impacts, architects and specifiers are encouraged to request environmental product declarations and to seek energy modeling information as available.


1 Consult George Wypych, Handbook of Foaming and Blowing Agents, 2017.

2 Refer to the Federal Emergency Management Agency’s (FEMA’s), Flood Damage-Resistant Materials Requirements for Buildings Located in Special Flood Hazard Areas in Accordance with the National Flood Insurance Program, Technical Bulletin 2, August 2008.

3 Review Honeywell, Insulation and Waterproofing for Metal Buildings and Metal Roof Systems: The Case for Using Better Insulation and Waterproofing Technologies in Metal Roof Systems and Metal Buildings.

4 Refer to Architectural Testing, Performance Test Report Rendered to Spray Polyurethane Foam Alliance, Project: Racking Load Tests, 2007.

  1. [Image]:
  2. HFCs:
  3. HFOs:
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  5. foam blowing agent:
  6. 0.055 to 0.11:
  7. GWP value:
  8. global warming impact:
  9. 0.5 C (32.9 F):
  10. the use of HFOs:
  11. ozone depleting chemicals:
  12. [Image]:
  13. states:
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  15. uplift for wood roof sheathing panels:
  16. National institute of Standards and Technology (NIST):
  17. two things:
  18. product selections:
  19. modeling:

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