a method for providing a container with one or more layers of barrier material during the production of the container from a thermoplastic . a preform is stretched in its axial direction , generally an amount corresponding to the total axial stretching required for conversion of the preform to a container , after which the stretched preform is provided with one or more barrier layers , and the preform is then heated and converted to a container . in one embodiment , the axially stretched preform is produced by assembling axially stretched part - preforms covered with one or more barrier layers . the combined preform is then converted to a container .