The company that invented OSB sheathing now offers a version it says is nearly three times more burn-resistant than a conventional wood panel. LP says each panel of FlameBlock Fire-Resistant OSB Sheathing is coated with a layer of noncombustible magnesium oxide plus 1/2 gallon of crystallized water; the water becomes liquefied only if exposed to intense heat. FlameBlock carries a Class A flame spread rating, which makes it suitable for fire zones as well as party walls in multifamily construction. It costs two to three times as much as standard OSB. LP Building Products, 888/820-0325, lpcorp.com.