1st generation refrigerants Chlorofluorcarbons (CFCs)
2nd generation refrigerants Hydrochlorofluorocarbons (HCFCs)
3rd generation refrigerants Hydrofluorocarbons (HFCs)
4th and current generation refrigerants Hydrofluoro-olefins (HFO)
HFOs are being increasingly used. HFOs have low global warming potentials, typically under 150. Many of them, however, are also classified as A2L refrigerants (mildly flammable) and industry needs to adapt its practices to maintain a high level of safety.
Hydrocarbons, ammonia and CO are also increasingly used as refrigerants. They have a very low (or zero) GWPs, but there are issues of extreme flammability, toxicity and high pressure. All refrigerants have their place, and they all need to be used appropriately by trained technicians.