also used. All these have the principle disadvantage of being quite flammable. Nitrous oxide is also used as a propellant to deliver foodstuffs (e.g. whipped cream ). Medicinal aerosols such as asthma inhalers use hydrofluoroalkanes (HFA): either HFA 134a (1,1,1,2,-tetrafluoroethane) or HFA 227 (1,1,1,2,3,3,3-heptafluoropropane) or a combination of the two.