In packaging, a means of forming hollow plastic packaging (such as bottles) in which air or nitrogen is "blown" into preformed plastic, causing the plastic to expand against the mold corresponding to the desired shape of the bottle. Blow molding can be performed either by injection molding (in which melted plastic is injected into a cavity around a core rod and air used to expand the plastic to the desired shape) or extrusion molding (in which the melted plastic is extruded as a tube, the mold being placed around it to form the desired shape).
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