Refrigerants are substances used in cooling systems, such as air conditioners and refrigerators, to absorb and release heat. They change from liquid to gas and back again, allowing them to transfer heat effectively. Common refrigerants include R-134a and R-410A, each with specific properties that make them suitable for different applications. The choice of refrigerant is important for energy efficiency and environmental impact. Some refrigerants, like CFCs (chlorofluorocarbons), have been phased out due to their harmful effects on the ozone layer. Newer alternatives, such as HFCs (hydrofluorocarbons), are being used, but they also have global warming potential, leading to ongoing research for more sustainable options.