A method of forming a blow molded plastic article wherein the article comprises an airflow conduit, comprising: providing a first sheet of insulation material located on a insulation carrier; providing a blow molding mold including two halves and having a molding surface defining a molding cavity to form the article; locating the insulation carrier between the two halves of the blow molding mold; transferring the first sheet of insulation material from the insulation carrier to the blow molding mold; introducing an extrudate of thermoplastic composition between the two halves of the blow molding mold; closing the blow molding mold; forming the extrudate to a shape of the mold cavity of the blow molding mold to form the article; and bonding the extrudate to the first sheet of insulation material as the extrudate is being formed to the shape of the mold cavity.