Outer: FR-treated cotton. Liner: FR-treated cotton with 3M Thinsulate Platinum Insulation Flame Resistant. Thread made of Nomex® IIIA brand fiber. Meets ASTM F1506. ATPV=26 cal/cm². NFPA 70E/HRC=3. Flame Resistant for up to 50 washings. * Nomex® is a registered trademark of E.I. du Pont de Nemours and Company.