A mold assembly for blow molding comprises mating mold components having opposed mating surfaces and each comprising an insert defining the exterior of a neck portion of the article to be molded and at least one heat pipe located with one end thereof proximate a molding surface and the other end thereof in the interior of a heat transfer fluid conducting passage within the mold component. Advantageously, each mold component includes sealing means effective to prevent passage of fluid from the mold component around heat pipes passing through walls thereof. Advantageously, each insert includes at least one knife insert for forming a parting groove for separating waste of the article as molded from the neck portion comprising a finished article. A blow molding machine comprises a mold assembly in accordance with the invention. Advantageously the molding machine comprises trimming means for parting the molded article at the parting grooves.