HFO vs Traditional Closed Cell Spray Foam: What's the Difference?

Not all closed cell spray foam is the same. The blowing agent (the gas that creates the foam's cell structure) determines both the R-value and the environmental impact of the product. HFO-blown foam is a significant step forward on both counts. Here's what separates it from traditional HFC-blown closed cell foam.

What Is a Blowing Agent?

Spray polyurethane foam is created when two chemical components react and expand. The expansion is driven by a blowing agent, a gas that forms the bubbles that become the foam's cell structure. In closed cell foam, those bubbles are sealed shut, and the gas trapped inside contributes significantly to the foam's thermal resistance.

The blowing agent matters for two reasons: it directly affects the R-value of the foam, and it has its own environmental impact measured as Global Warming Potential (GWP).

HFC-Blown Foam: The Old Standard

For decades, closed cell spray foam was blown with hydrofluorocarbon (HFC) blowing agents, most commonly HFC-245fa. These delivered good R-values in the R-6.0 to R-6.5 per inch range and became the industry standard for closed cell insulation.

The problem: HFCs are powerful greenhouse gases. HFC-245fa has a Global Warming Potential of 1,030, meaning one pound of it released into the atmosphere has the same warming effect as 1,030 pounds of CO2. The spray foam industry came under pressure from green building programs and regulators to find a better solution.

HFO-Blown Foam: The New Generation

Hydrofluoroolefin (HFO) blowing agents, specifically Honeywell's Solstice Liquid Blowing Agent (Forane 1233zd), were developed to solve the GWP problem. The result is a blowing agent with a GWP of just 1 (equivalent to CO2 itself) while delivering superior R-value performance.

ThermoSeal HFO uses Forane 1233zd(E), which achieves an R-value of 7.4 per inch, higher than any HFC-blown product on the market. The HFO molecule is larger and less thermally conductive than HFC, which is why it performs better thermally even as it eliminates the environmental liability.

Side-by-Side Comparison

The R-Value Advantage Matters

The difference between R-6.5 and R-7.4 per inch may sound small but it compounds meaningfully over a full installation:

• To achieve R-49 in an attic with HFC-blown foam: approximately 7.5 inches required
• To achieve R-49 with ThermoSeal HFO: approximately 6.7 inches required

In a retrofit application with limited rafter depth, that 0.8-inch difference can mean the difference between hitting code and falling short. In a commercial roofdeck application at scale, the reduced material volume translates directly to lower installed cost per square foot.

No Ignition Barrier Required

One practical advantage of ThermoSeal HFO that often surprises installers and building officials: it does not require an ignition barrier or thermal barrier in certain applications where HFC-blown foams do.

Per IAPMO ER-0698, ThermoSeal HFO can be left exposed in crawl spaces and attics under specific conditions without requiring an additional thermal or ignition barrier coating. This simplifies installation, reduces labor cost, and eliminates a material that HFC-based alternatives require.

Regulatory Pressure on HFCs

The EPA's American Innovation and Manufacturing (AIM) Act authorizes the phasedown of HFCs across all sectors, including building materials. HFC-245fa and similar blowing agents are scheduled for significant production reductions through 2036. The practical implication: HFC-blown spray foam will become more expensive and eventually unavailable as the phasedown progresses.

HFO-blown products like ThermoSeal HFO are fully outside the scope of HFC phasedown regulations. Specifying HFO today is specifying a product that will remain available and competitively priced as HFC alternatives are phased out.

What About HFO Cost?

HFO-blown foam does carry a modest premium over HFC products, typically 10 to 15 percent higher on material cost. However, the higher R-value per inch means less material is needed to achieve the same code-minimum R-value, which offsets a portion of the cost premium. In many applications, the net installed cost difference is minimal.

When LEED points, green building certifications, or owner sustainability requirements are part of the project scope, HFO often becomes the financially obvious choice even before considering performance advantages.

Which Should You Specify?

For most residential and commercial applications in 2026, ThermoSeal HFO is the right choice. The R-value advantage, regulatory future-proofing, no-ignition-barrier exemption, and low GWP make it the highest-performing and most future-proof closed cell product available.

ThermoSeal 5G is a strong second choice when project budgets are constrained and GWP requirements are not a factor; it delivers nearly identical thermal performance at a lower price point.

The right product for your project depends on application, climate zone, local code requirements, and budget. A ThermoSeal certified installer can help you choose and provide all necessary documentation for code review and green building certification.