A polymer thin film includes polyethylene having a weight average molecular weight of at least approximately 500,000 g/mol, where the thin film is characterized by transparency within the visible spectrum of at least approximately 80%, bulk haze of less than approximately 5%, and an in-plane elastic modulus of at least approximately 10 GPa. The polymer thin film may be thermally conductive and may be incorporated into an optical element and configured to dissipate heat, such as from a light-emitting device.