A surfactant composition is disclosed comprising branched alkyl sulfate having 8 to 12 carbon atoms; optionally a linear alkyl sulfate having 8 to 12 carbon atoms; and optionally an alkyl ether sulfate having 8 to 13 carbon atoms. A gypsum slurry or gypsum board core is disclosed comprising gypsum, water, and a surfactant composition as described above. The foam voids in the core have a greater median diameter than foam voids made with corresponding linear alkyl sulfate. A method of controlling the median foam void diameter in a gypsum board is disclosed. A first foam water composition is provided comprising a linear alkyl sulfate surfactant. A second foam water composition is also provided comprising a branched alkyl sulfate surfactant. The proportions of the first and second foam water compositions employed in a gypsum composition are selected, or if desired changed, to provide the desired median foam void diameter.