USG Sheetrock® Brand Mold Tough® Gypsum Liner Panels have a noncombustible, moisture- and mold-resistant gypsum core that is encased in moisture- and mold-resistant, 100 percent recycled blue face and back papers. The panels are UL Classified as to fire resistance (Type SLX) and feature double beveled edges for easy installation. Panel may be substituted for USG Sheetrock® Brand Gypsum Liner Panels in all Shaft Wall and Area Separation Firewall systems.