WINFLEX THHN WIRE 3.5MM2 X 150 METERS 12/7 STRANDED BLACK ==================================== BLACK THHN (Thermoplastic High Heat-resistant Nylon-coated) wire is designed with a PVC (polyvinyl chloride) insulated nylon sheath. Most THHN building wire comes with the dual rating THHN/THWN, meaning it is usable in both wet and dry conditions, as well as both indoor and outdoor use.