PURPOSE: To obtain an inorganic glass foam, having a low bulk specific gravity, fine bubbles and a firm structure and suitable as a building material or a member for various materials.

CONSTITUTION: One or more artificial lightweight materials or one or more natural lightweight materials are added to a slurry prepared by adding an alkaline component, a foaming agent and water to inorganic glassy mineral grains or a paste obtained by heating the resultant slurry (or slurry) and the obtained mixture is then uniformized by stirring, etc. The uniformized mixture is subsequently pressurized or dried at ≤350°C temperature without pressurizing, subsequently burned and foamed.