Rapid re-launch aerospace vehicles require materials with high specific strength to withstand thermal shock associated with repeated re-entry. Glass fiber reinforced polyester (GRP) composites have rapidly become preferred for high value structural components requiring high specific strength. Their ability to sustain high tensile and impact loads has allowed them to be used as light-transmitting panels and fuselages. Due to service conditions, heat flux strongly alters mechanical properties with exposure time. The effect of including a thermal-barrier coating, in the form of a carbon nanopaper, on the monotonic flexural properties of a GRP composite is analyzed. A series of three-point bend experiments was performed on specimen-sized samples of composites subjected to various levels of heat fluxes across numerous exposure times. Analysis of these experiments reveals trends in the deformation mechanisms of these materials near failure. Correlations of flexural modulus and critical load are used to develop associations to strength.