A refrigerant is a heat transfer medium – a substance that can absorb heat from a source, transport it and release it elsewhere. The transfer might be used to cool the source or warm the destination, or both.

The name comes from where you’d expect: refrigerators absorb unwanted heat from the storage compartment, pump it to external pipes which dissipate it to air. The same cooling method is used in air conditioners. Domestic heat pumps use the principle to warm rooms or water.

Other physical properties of refrigerants find applications beyond heat transfer. In particular some make good aerosol propellants, used in spray cans, fire extinguishers, insulation foam manufacture, and notably in “metered dose inhalers” to control asthma and other breathing problems.