RM-04-BR, a mock material for the plastic-bonded HMX-based explosive LX-04, is characterized after being thermally damaged at 140 degrees C and 190 degrees C. We measured the following material properties before and after the thermal experiments: sample volume, density, sound speed, and gas permeability in the material. Thermal treatment of the mock material leads to decoloring and insignificant weight loss. The sample expanded, resulting in density reductions of 1.0% to 2.5% at 140 degrees C and 190 degrees C, respectively. Permeability in the mock samples was found to increase from 10(-16) to 10(-15) m(2), as the porosity increased. The permeability measurements are well represented by the Blake-Kozeny equation for laminar flow through porous media. The results are similar to the gas permeability in PBX-9501 obtained by other researchers [1, 2].