The present invention includes polymer films that comprise lanthanum hexaboride and an epoxy agent. The lanthanum hexaboride and epoxy agent can be incorporated into or onto a polymer film in any suitable manner. The addition of an epoxy agent surprisingly provides a stabilization effect to the lanthanum hexaboride, which allows for the production of polymer films that advantageously absorb infrared radiation and resist environmental degradation. Polymer films thus produced have a significant number of applications, for example, but not limited to, display devices, protective coverings, and glazing film applications.