HFOs (hydrofluoro-olefins) are the fourth generation of fluorine-based gases. HFC refrigerants are composed of hydrogen, fluorine and carbon atoms connected by single bonds between the atoms. HFO refrigerants are composed of hydrogen, fluorine and carbon atoms but contain at least one double bond between the carbon atoms.
The first HFO, jointly developed by DuPont and Honeywell, is HFO 1234yf which is sold under the brand names Opteon YF and SOLSTICE yf. This is a low GWP (Global Warming Potential) replacement for R134a for use in mobile air conditioning (MAC) systems in the automotive sector.