Abstract: An intimate mixture of an amorphous silica potassium oxide, boric oxide, alumina and a cellulating agent is subjected to a temperature of between 1390.degree. C. to 1450.degree. C. for a sufficient time to coalesce the mixture and gasify the cellulating agent and form a cellular body. The mixture is prepared by first forming a slurry and, drying the slurry to form aggregates, and are thereafter comminuted if necessary to form a pulverulent batch. The pulverulent batch is heated in a cellulating furnace to a foam-like mass which is comminuted to form a precellulated material. The precellulated material is mixed with additional cellulating agent and pulverulent batch in preselected proportions and heated in a furnace to gasify the cellulating agent to form a cellular body. Alternatively alumina, boric oxide, an alkali metal salt and a cellulating agent are comminuted and mixed in a ball mill. Thereafter, amorphous silica is added to form a mixture containing more than 80% silica.