The enhancement of many of the mechanical properties of thermoplastics which may be achieved by orienting the molecules has been known for some time. It has been exploited in the production of textile fibres end oriented films. Molecular orientation also occurs during processes such as extrusion, moulding or forming. Here, unless carefully controlled, it may well cause a deterioration in the properties of the finished article. In view of this a systematic study on the anisotropy of the mechanical properties of thermoplastics, resulting from molecular orientation, is being carried out at present in these laboratories … [cont.].