A method of making a closed-cell silica foam glass is provided which can include diffusing a substance into a porous glass substrate to form an impregnated substrate, sealing the impregnated glass substrate and heating to a first temperature, wherein the pressure is greater than one atmosphere, heating the container to a second temperature, wherein the second temperature is higher than first temperature, removing the solid glass, non-porous substrate, and heating the solid glass, non-porous substrate to a third temperature to soften the solid glass, non-porous substrate and thereby expand the solid glass, non-porous substrate. A closed-cell silica foam product is provided which can have a closed-cell structure and high temperature insulating property.