Magnum Building Products - World Leader in Magnesium Oxide Board (MgO Board) magnesium oxide board,mgo board,backer board,gypsum,EIFS,crystallized glass,magnum stone,wallboard,sheetrock,sheathing,mold resistant,mildew resistant,underlayment,wholesale,construction,gyp board Magnum Building Products is the world leader in high-quality Magnesium Oxide Board (MgO Board) used in place of gypsum for interior and exterior wall construction. Magnum BP also carries crystallized glass, window sills, sills, panels, SIPS, hardware, doorstops, etc.