Abstract: Thermally insulating materials (TIMs) for use in concentrated solar thermal (CST) technologies comprising a mesoporous oxide including a porous oxide matrix comprising a porous oxide and a metal oxide or metal nitride in the form of a conformal layer of the metal oxide or metal nitride on the surface of the porous oxide matrix, wherein the conformal layer completely covers the surface area of the porous oxide matrix, or in the form of metal oxide or metal nitride nanoparticles dispersed throughout the porous oxide matrix, or in the form of a conformal coating or nanoparticles, methods of preparing same, and solar devices comprising same.