HFO vs HFC Spray Foam: Blowing Agents and the EPA Rules

What a blowing agent does

The real difference in HFO vs HFC spray foam is one ingredient: the blowing agent. Closed-cell foam starts as two liquids. The blowing agent rides in the B-side resin as a liquid. When the two sides meet at the gun, the reaction heat boils it into tiny bubbles that the hardening plastic seals in place. The Spray Foam 101 page walks through it step by step.

That trapped gas does much of the insulating, so the blowing agent matters long after the foam cures. Honeywell lists its HFO blowing agent, HCFO-1233zd(E), with a vapor thermal conductivity of 10.2 mW/m·K at 20°C and a boiling point of 66°F (19°C). Many formulas also use a little water, which reacts to make carbon dioxide and helps the rise.

HFO vs HFC spray foam: four generations of blowing agents

HFOs are the fourth generation in a long phase-out:

A naming note: 1233zd(E) contains chlorine, so EPA calls it an HCFO. Its ozone depletion potential is so small that Honeywell lists it as approximately zero, and it breaks down in the atmosphere in about 26 days. The two GWP figures come from different scientific sources: EPA's reference table, based on WMO 2022, lists 4, and Honeywell lists 1.

The federal rules, in order

CFCs and HCFCs. These were phased out under the Montreal Protocol because they damage the ozone layer. U.S. CFC production ended in 1996. EPA's phase-out schedule ended production and import of HCFC-141b, a widely used foam blowing agent, in 2003.

HFCs. HFCs don't harm the ozone layer, but they are powerful greenhouse gases. EPA's SNAP program listed several HFCs as unacceptable in foam, but a 2017 federal court decision (Mexichem Fluor v. EPA) struck down part of those rules, and several states wrote the limits into their own regulations. Congress then passed the AIM Act in December 2020, giving EPA direct authority to phase down HFCs.

The Technology Transitions rule. EPA finalized it in October 2023. For polyurethane foam, including pre-blended polyol products like spray foam resin, the GWP limit is 150. Systems above that couldn't be manufactured or imported from January 1, 2025, and sale, distribution and export end three years later, on January 1, 2028. EPA's sector table lists no separate installation date for foam.

What changed since. In May 2026, EPA finalized a reconsideration of parts of the rule. It covered refrigeration and air-conditioning subsectors; foam was not among them, so the foam dates stand.

State HFC rules and Pennsylvania

Several states adopted their own HFC rules while the federal SNAP limits were tied up in court. By 2022, California and Washington had gone further than the old SNAP rules, and Colorado, New York, Maine, Vermont, New Jersey, Delaware, Rhode Island, Maryland and Massachusetts had adopted rules aligned with them.

Pennsylvania did not. A 2022 industry summary listed it among states that had expressed intentions without passing a law, and we found no Pennsylvania HFC rule in effect. The federal rule governs here. For our customers in Chautauqua County, New York has its own HFC regulation, but with the federal 150 limit in place, closed-cell systems made since 2025 have to use low-GWP blowing agents everywhere in the country.

Performance: what actually changed

R-value. A lower-conductivity gas helps, but cell size, density and the rest of the formulation also matter. Current HFO closed-cell data sheets list aged values from about R-6.3 to R-7.4 per inch, and some list a different per-inch value for thin and thick layers. Compare products by their aged R-value at the thickness you are buying, from the technical data sheet. R-value per inch explains the spread, and our notes on one HFO closed-cell product walk through an example.

Lift thickness. This comes from the formulation, not just the blowing agent. One current HFO product allows up to 4 inches per pass; a high-lift product allows 6.5 inches at 70°F or cooler, but only 3.25 inches above 80°F.

Spraying in cold weather. The temperatures a foam can be sprayed at are also set by the formulation. Some winter-grade HFO products are rated for surfaces down to about 15 to 20°F, which is what makes spraying through a Western Pennsylvania winter possible.

Cold-weather R-value in service. A blowing agent with a high boiling point can start to condense inside the cells near freezing, which lowers the foam's insulating value at that temperature. In a 2022 conference paper, Arkema (a maker of 1233zd(E)) reported that effect at 32°F in lab foams blown with HFO-1336mzz(Z), the higher-boiling of the two main HFOs; all the HFOs it tested performed similarly at 50°F and 75°F. The aged R-value on each product's data sheet is still the fairest number to compare.

Flammability. Honeywell lists HCFO-1233zd(E) as non-flammable. The finished foam still needs the same thermal barrier or listed coating as any spray foam.

What to ask a contractor

• Which product will you spray, and what blowing agent does it use?
• What is the aged R-value at the thickness you are quoting, per the data sheet?
• Can I see the drum labels, lot numbers and expiration dates? FoamGuard records drum lot numbers on every job. See spray foam shelf life and storage.
• Are you certified by the manufacturer, so the product warranty can be registered? Our contractor guide covers the red flags.

Want a number for your own project? Price My Project or call (814) 208-3478.