an elongate , rigid , tubular , biaxially oriented thermoplastic , hollow thin - walled shaped article is molded by introducing into an elongate mold cavity , the internal configuration and dimensions thereof corresponding to the exterior surface area of the desired shaped article , and aligning along the longitudinal axis thereof , a hollow tubular thermoplastic preform heated to the biaxial orientation temperature of said thermoplastic ; expanding under internal pressure said heated preform to simultaneously , both longitudinally and transversely , uniformly stretch same , at least to the natural biaxial drawing ratio thereof , but to a value in the transverse direction of less than 100 % of that ultimately desired ; next further expanding said heated preform , under increased internal pressure , completely against the internal walls of the mold cavity to thus completely shape said ultimately desired shaped article ; and then cooling said desired shaped article and releasing all pressure therefrom .