The thermal conductivity of two novel polyurea/silica ORMOSILs (Organically Modified Silicates) created for use in high temperature optical applications. The purpose of these new materials was to replace the materials currently in use which start to degrade in high temperature situations. The transmission/absorption, refractive index, thermal conductivity, and thermal stability of the new materials was investigated to determine their suitability. The thermal conductivities measured were 0.26 and 0.27 W/mK ...