The properties of metal thin films have been largely overlooked in discussions of the technical limitations and problems that arise in the field of direct detection of exoplanets. Here, polarization properties and anisotropy properties of highly reflecting thin metal films are examined within the context of the requirements for the ultralow-scattered-light system performance of coronagraphs applied to space and ground-based high-contrast, whitelight astronomy. Wavelength-dependent optical constants for highly reflecting thin metal films, taken from the literature, are used to calculate the polarization-dependent transmissivity of a typical coronagraph. The effects of degraded performance on the astronomical science are examined. Suggestions are made for future work.