Abstract: This invention relates to a method for manufacturing a surface-treated particulate inorganic material, and more particularly to methods for manufacturing lightweight particulate inorganic materials, such as expanded perlite or expanded clay, coated with one or more silsesquioxanes. The surface-treated particulate inorganic material according to the present invention is suited for introduction into construction materials, such as mortar, piaster, cement and lightweight concrete, to lower the loose bulk density and improve the mechanical strength of the mixture.