coatings u201d and similar phrases herein are intended to include selectivity at non solar wavelengths as appropriate nanostructured selective absorption layers as described above although they can provide very large a e ratios are still subject to mechanical thermal and environmental degradation as a result another aspect of the present invention is to seal the nanostructured selective absorption layer by encapsulating it with a sol gel layer a sol gel layer is composed primarily of a network of highly polymerized monomers the monomers are typically oxides of network forming elements e g al b mg si ti and zr although other network forming elements can be used bridging atoms other than oxygen can also be found in sol gel materials the sol gel layer provides physical and chemical protection to the nanostructured selective absorption layer in a particular implementation of the present invention a body whose surface has previously been covered with a nanostructured selective absorption layer is coated with a low viscosity sol solution by dipping the body into a bath of the sol solution a sol solution generally comprises a solvent which holds in solution a distribution of monomers and small polymers of the network forming oxides these monomers and small polymers have terminal chemical groups which are conducive to their combination into larger polymers and to bonding with the surface and the nanostructured selective absorption layer the viscosity of the sol solution is controlled by the amount of solvent in.