A composite fabrication method is reported that incorporates silicones into bulk aspen substrates and subsequently crosslinks the additives in situ. This process utilizes supercritical CO2, a non-toxic and easily recoverable solvent, as a transport and reaction medium resulting in aspen composites that have been uniformly infused with silicone. Flexure properties of aspen-silicone composites were determined to be indistinguishable from those of aspen. However, after thermal degradation, the residual flexure properties of the composite char were significantly improved compared to the virgin aspen char. Energy release rate, total energy released, and char yield of aspen and aspen-silicone composites were measured and a significant improvement in all three of these fire-resistance parameters was observed after the incorporation of silicone. Samples were also exposed to a controlled thermo-oxidative environment under an applied stress to measure lifetimes of each sample at given temperatures and stress levels. This data were subjected to an Arrhenius analysis and show a good linear correlation. Composite systems demonstrate significantly longer lifetimes than virgin aspen and the slopes of all lines are nearly identical, suggesting that no change in the chemical degradation mechanism has occurred.