The changes in the molecular network of several grades of polyethylene subjected to high pressure annealing are followed using a simple model which combines thermal expansion and mechanical measurements. It is found that annealing reduces the degree of molecular entanglement, particularly when performed well within the intermediate hexagonal phase. It is shown that this process can be used to improve the drawability and hence the ultimate physical properties of high molecular weight material. In low molecular weight material it is necessary to retain a sufficiently intact network which can orient the crystallites effectively and which prevents the material from becoming friable.