Cellular catalyst supports gain an increasing importance for exhaust gas treatment and environmental catalysis. In combination with photocatalytical active components, a high light transmittance is necessary for high-efficiency activation. In order to obtain optically suitable glass foams, a novel process was developed based on the use of a preceramic polymer. During thermal decomposition, the polymer provides highly dispersed silicon dioxide (SiO2), which simultaneously reacts with a glass modifier to form a borosilicate glass. Because of a low processing temperature of 1050 degrees C or less, the open-cellular structure was retained and is therefore suitable for coatings and applications where high permeability and optical transmittance are required.