A Discussion of Heat Mirror Film: Performance, Production Process, and Cost Estimates

A unique, transparent, electrically conductive plastic film is produced in commercial quantities by the Sierracin Corporation. This film is designated by the trade name Intrex and has been commercially available for several years. It was originally developed as a component in electrically heatable, transparent products such as de-icing windshields for aircraft, locomotives, and the like.

The electrical conductivity is imparted to the plastic film by the vacuum deposition of a thin film of gold onto one surface. This gold film exhibits typical luminous transmittance of 80% and sheet resistivity of 10 ohms per square. The free electron concentration in the gold film that permits such high electrical conductivity is also responsible for very high reflectance and low emittance of electromagnetic radiation in the near and middle infrared spectral regions. For this reason the Intrex film can be regarded as a heat mirror with possible application as a glazing cover interior to a conventional window where it serves to reflect low temperature, long wavelength radiation back into the interior of the heated space or prevent its radiation outward. Since the chief utility of such a heat mirror film is during the heating season, a high luminous transmittance, or more precisely a high solar transmittance, is essential to ensure the benefits of solar heat gain, Sierracins Intrex film appears to exhibit a very favorable combination of infrared reflectance and solar transmittance and is therefore the subject of the inquiry by the Lawrence Berkeley Laboratories of the Department of Energy as to further related technical and economic factors, which constitute the substance of this report.