A method of forming a blow molded plastic article comprising: providing an insulation carrier; providing a first sheet of insulation material located on the insulation carrier; providing a blow molding mold, the blow molding mold including two halves (222a, 222b) and having a molding surface defining a molding cavity to form the blow molded plastic article, wherein the blow molded plastic article comprises a blow molded airflow conduit; 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 such that the first sheet of insulation material overlies at least a first portion of the molding surface of the blow molding mold; introducing an extrudate of thermoplastic composition between the two halves (222a, 222b) 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 blow molded plastic article; bonding the extrudate to the first sheet of insulation material overlying at least a portion of the mold surface of the blow molding mold as the extrudate is being formed to the shape of the mold cavity; and forming at least one air inlet and at least one air outlet in the blow molded airflow conduit; characterized in that the insulation carrier comprises a first insulation carrying mandrel; and providing a first sheet of insulation material located on the insulation carrier further comprises forming the first sheet of insulation material on the first insulation carrying mandrel; and wherein forming the first sheet of insulation material on the first insulation carrying mandrel is performed after heating the first sheet of insulation material. providing an insulation carrier; providing a first sheet of insulation material located on the insulation carrier; providing a blow molding mold, the blow molding mold including two halves (222a, 222b) and having a molding surface defining a molding cavity to form the blow molded plastic article, wherein the blow molded plastic article comprises a blow molded airflow conduit; 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 such that the first sheet of insulation material overlies at least a first portion of the molding surface of the blow molding mold; introducing an extrudate of thermoplastic composition between the two halves (222a, 222b) 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 blow molded plastic article; bonding the extrudate to the first sheet of insulation material overlying at least a portion of the mold surface of the blow molding mold as the extrudate is being formed to the shape of the mold cavity; and forming at least one air inlet and at least one air outlet in the blow molded airflow conduit; characterized in that the insulation carrier comprises a first insulation carrying mandrel; and providing a first sheet of insulation material located on the insulation carrier further comprises forming the first sheet of insulation material on the first insulation carrying mandrel; and wherein forming the first sheet of insulation material on the first insulation carrying mandrel is performed after heating the first sheet of insulation material.