A gas uster, also erroneously referred to as canned air, is a product consisting of liquefied difluoroethane, trifluoroethane, or tetrafluoroethane in a spray can, with a long nozzle that enables the user to direct a precisely focused blast of gas. Gas dusters do not use compressed air, but other inert gases that are much easier to compress into a liquid state. Hydrocarbons, like butane, were often used in the past, but their flammability forced manufacturers to use fluorocarbons.