Heat transmission through a layered compound material consisting of carbon steel backing and insulation (either aluminized silver or fiberglass) was examined to determine thermal properties. The heat flux impinged on the insulation material side of this simulated "firewall." A heat transfer model was developed that could, in principle, be used to predict the heat transfer through layered compound materials using techniques of thermal property parameter estimation. The parameter estimates are based on thermocouple measurements of surface temperatures during heating on both sides of the material. The experiment analyzed in this article involved a vertical plate exposed on the insulation side to a transient step-applied radiant heatflux. The transient temperature measurements were fitted to heat transfer models. Thermal diffusivity and Biot number were estimated using ordinary least-squares nonlinear regression.