Don’t let the cold stop you from taking one last lap: the PhD® Nordic Medium sock delivers maximum warmth and breathability when the going gets cold. Built with long-distance comfort in mind, we’ve added our patent-pending Indestructawoolâ„¢ technology for ultimate durability and our 4 Degreeâ„¢ elite fit system to create one of our best-fitting Nordic wool socks that won’t bunch, slip, or bind.Â