Aerogels are highly porous solids prepared by sol-gel processing and supercritical evacuation. Because of their high surface area, aerogels can be used as an effective catalyst for the thermal decomposition of many gaseous compounds. A variety of hydrocarbon gases have been chosen to deposit carbon in the aerogel matrix, with the deposition temperature varying from 500° to 850°C depending on the hydrocarbon used. The amount of carbon that can be deposited in the aerogel is surprisingly large, reaching up to 10 times the original weight after extensive deposition using acetylene. Overall, the aerogel composites prepared have a uniform microstructure with the average particle size in the nanometer range. In addition, we have observed some interesting graphitic structures including carbon nanotubes and rings of various shapes. Carbon deposited in the aerogel can reduce infrared transmission of the material as well as volume shrinkage at elevated temperatures, thereby improving its thermal performance.