Simpson Racing CarbonX�� Ultimate��� UnderwearLong Sleeve - XLCarbonX Ultimate underwear is made from double jersey interlock knit comprised of a patented blend of high performance fibers and has extraordinary thermal protective properties. It is inherently flame resistant, will not burn, melt, or ignite when subjected to direct flame. Nomex or CarbonX Underwear underneath a racing suit will dramatically improve Thermal Protection Performance (TPP) in the case of an accident involving fire.