Hollow glass microspheres (62) made from a low heat conductivity glass composition containing a high vacuum and a thin metal coating (63) deposited on the inner wall surface of the microspheres are described. The hollow glass microspheres are used to make superior insulation materials in the construction of highly efficient solar energy collectors. The hollow glass microspheres can also be made to contain a thin transparent or reflective metal coating deposited on the inner wall surface of the microspheres by adding to the blowing gas small dispersed metal particles and/or gases of organo-metal compounds and decomposing the organo-metal compounds. The hollow glass microspheres can be made from low heat conductivity glass compositions. The microspheres can be used to make improved insulation materials and composites and insulating systems, and panels (61). The hollow glass microspheres can be used as filler materials in plastics, in plastic foam compositions and in concrete and asphalt compositions. The hollow glass microspheres can also be made in the form of filamented glass microspheres with a thin glass filament connecting adjacent glass microsphere.