Abstract: The conventional process of manufacturing hollow bodies with multi-layer walls using extrusion and blow molding techniques is improved by first making a preform of a thermoplastic carrier layer with an adhesive layer on one or both sides and then applying the additional layer or layers to the adhesive layer(s) in a separate operation. The additional layer(s) has properties different from the carrier layer and serves as an insulation or barrier layer to shield the carrier layer from substances to be contained by or which will surround the hollow body. Among other advantages, the improved process allows recycling of waste and surplus preform material, stronger heat-seal seams in the hollow bodies, less complicated extrusion equipment and more economic use of expensive barrier layer materials.