The Milspec 10' Pro Power SJTW Black Extension Cord has become the industry standard for durability and safety. It features a soft-drawn, bunch stranded 100% copper conductor for maximum flexibility. In addition, the heavy duty plugs are molded with large strain reliefs that prevent the ends from pulling away from the body. The cords are manufactured with cold weather insulating and jacketing compounds. As a result, Pro Power cords are extra flexible in temperatures well below freezing.