The method of applying a heat reflective coating to a substrate sheet of construction material is directed particularly to the coating of insulation material, such as fiberglass batts, at the time of manufacture. However, it may be applied to virtually any flat, planar sheet of material in order that the material may provide insulation as well as structural value. The present method provides numerous benefits. The insulation properties of the material are improved by the addition of the heat reflective coating thereon. Economies of scale are achieved by coating the materials at the time of manufacture, or at least at some centralized location. By completely encapsulating fibrous insulation with an impervious coating, the emission of irritant fiber particles from the insulation and corresponding health hazards are eliminated. Also, the efficiency of the insulation is improved by sealing out moisture when the insulation is completely encapsulated by the coating.