An approach is presented for modeling the thermal expansion boundary layer in energetic materials such as solid propellants and explosives during their combustion. A thermodynamically consistent system of conservation laws is presented that describes the thermo-elastic. solid with a temperature-dependent thermal expansion coefficient in order to study the role of thermal expansion in heat transfer and deformation in a thin layer adjacent to the combustion zone. It is shown that the thermal expansion can produce an effect that absorbs energy near the burning surface and can significantly reduce the temperature in a small layer. The analysis given here is also relevant to the technologically important problem of laser ablation of materials, but the discussion is focused on application to propellant combustion.