Wikipedia
Hydrofluoroolefin
Hydrofluoroolefins (HFOs) are chemical compounds composed of hydrogen, fluorine and carbon. They are distinguished from hydrofluorocarbons (HFCs) by being derivatives of alkenes (olefins) rather than alkanes.
HFOs are being developed as "fourth generation" refrigerants with a thousand time lower global-warming potential than HFCs. HFOs currently in use include 2,3,3,3-tetrafluoropropene (HFO-1234yf) and 1,3,3,3-tetrafluoropropene (HFO-1234ze). 1-Chloro-3,3,3-trifluoropropene (HFO-1233zd) is also under development.