The Kazbek Z87+ safety glasses were designed for long days and demanding conditions. These uncompromising work sunglasses have an unmistakable lifestyle shape and polarized lenses. The Kazbek's frame is constructed of a nylon composite material that can be tied into a knot. And while we don’t recommend tying yours into a square knot， the rugged flexibility of the frame means you get a comfortable， yet virtually indestructible， pair of Z87+ safety glasses or polarized work sunglasses. A thermoplastic rubber (TPR) nosepiece offers a comfortable， non-slip fit.