Thermally conductive films, composite materials including the films, and electrothermal heaters including the films, are disclosed. The films include a polymer and a sufficient concentration of hexagonal boron nitride to provide adequate heat transfer properties, and have high thermal conductivity, peel strength, and shear strength. The films can include thermoset polymers, thermoplastic polymers, or blends thereof, and can also include electrically conductive materials, reinforcing materials such as fiberglass, carbon fiber, metal mesh, and the like, and thermally conductive fillers, such as aluminum oxide, aluminum nitride, and the like. The films can be included in composite materials. The films can be used as part of a layered structure, and used in virtually any application, for example, various locations in aircraft, where heating is desirable, including nacelle skins, airplane wings, heated floor panels, and the like. The electrothermal heaters provide a more even heat, and a more rapid heat, than current resistive heaters formed from metal foils adhered to an adhesive film.