Refrigerants undergo a phase change between liquid and gaseous states within the refrigeration cycle, exploiting latent heat. Classic CFCs and HCFCs were banned due to their ozone depletion potential. Today, HFCs such as R410A and R32 dominate, with growing use of natural refrigerants like R290 (propane), R744 (CO₂), and R717 (ammonia). The EU F-Gas Regulation mandates stepwise reductions in global warming potential (GWP). Refrigerants are named according to ASHRAE nomenclature and classified by safety class (A1 to B3). Key properties include GWP, boiling point, pressure level, toxicity, and flammability. Handling is legally regulated and requires certified personnel.