a bond is created between a gypsum matrix and a silane - based sizing composition coated onto a glass fiber and gypsum matrix during manufacture of gypsum board . hydrophilic water extraction at the gypsum matrix - sizing interface reduces void formation and promotes the growth of smaller calcium sulphate dihydrate crystals within larger calcium sulphate dihydrate crystals in microstructurally identifiable regions adjacent to the glass fiber . the resulting gypsum board exhibits excellent strength , flexure resistance and nail pull out resistance . an alternative approach utilizes a silane based sizing composition having branched chains that diffuse into a wet gypsum mix . during gypsum cure , the diffusion triggers formation of pseudo polymeric networks in a microstructurally identifiable region adjacent to the glass fiber . bonds formed between the gypsum matrix and the silane based sizing composition increase the strength , flexure resistance and nail pull out resistance of the gypsum board .