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Sheetrock Brand Glass-Mat Panels Mold Tough VHI Firecode X (UL Type AR) are 5/8 in. (15.9 mm) Type X panels designed and tested to offer greater resistance to surface abrasion, indentation and impact damage than 5/8 in. (15.9 mm) Sheetrock Brand Glass-Mat Panels Mold Tough Firecode X. These abuse-resistant panels feature a noncombustible, moisture-resistant gypsum core that is encased in fiberglass face mats front and back that shed water. When tested in accordance with ASTM D3273, Standard Test Method for Resistance to Growth of Mold on the Surface of Interior Coatings in an Environmental Chamber, the panels score a 10 (highest). The fiberglass face is folded around the long edges to reinforce and protect the core, and the ends are cut square and even. The long edges of the panels are tapered, allowing joints to be reinforced and concealed with Sheetrock Brand joint treatment systems.