吹气成型又称中空成型，吹塑成型，是利用气体压力使闭合于模具中的热塑性塑胶吹胀成中空制品的成型方法，用于制造中空制品。

吹气成型的原理与吹制玻璃是一样的。 塑料颗粒加热融化形成型胚，置于对开模中，使型胚紧贴在模具内壁上，从而成型。

除了射出成型、押出成型外的第3种塑胶加工法。

Blow molding ( BrE moulding ) is a manufacturing process by which hollow plastic parts are formed. In general, there are three main types of blow molding: extrusion blow molding, injection blow molding, and injection stretch blow molding. The blow molding process begins with melting down the plastic and forming it into a parison or in the case of injection and injection stretch blow moulding (ISB) a preform. The parison is a tube-like piece of plastic with a hole in one end through which compressed air can pass.