HFOs

HFOs, or hydrofluoroolefins, are a class of fluorinated organic compounds that are characterized by at least one carbon–carbon double bond and fluorinated substituents. They are developed as low-global-warming-potential substitutes for hydrofluorocarbons (HFCs) in refrigeration, air conditioning, foam blowing, and other applications. The most widely used members are HFO-1234yf and HFO-1234ze; they have much lower global warming potentials than their HFC counterparts and zero ozone depletion potential. Chemically, HFOs are unsaturated fluorinated alkenes.

They generally have short atmospheric lifetimes and, as a result, low GWPs, though individual compounds vary. Some HFOs are mildly flammable (classified as A2L in many safety schemes), which affects handling, system design, and regulatory requirements.

Applications include refrigerants in automotive air conditioning (HFO-1234yf as a replacement for R-134a), small appliances and building air-conditioning equipment; foam blowing agents and insulating foams; and, in some cases, solvents and aerosols.

Environmental and regulatory context emphasizes reducing environmental impact by replacing high-GWP HFCs. HFOs provide zero ozone depletion potential and lower direct radiative forcing, but their flammability and suitability for specific systems require careful consideration. Regulation varies by region, with many jurisdictions promoting phase-downs or restrictions of high-GWP refrigerants and encouraging safer, lower-GWP alternatives. Standards organizations also provide guidelines for safe handling, leak testing, and material compatibility.

Limitations and outlook include addressing safety concerns related to flammability, cost, and supply stability. Ongoing research seeks nonflammable or even lower-GWP blends and new alternatives with favorable safety and performance profiles, alongside improved end-of-life management.