Don't let the cold stop you from taking one last run: the PhD Ski medium delivers maximum warmth and breathability when the going gets cold. Patent-pending Indestructawool technology provides ultimate durability to make sure your socks are ready to go, run after run. Made with our 4 Degree elite fit system for a sock that doesn't bunch, slip, or bind and a women's-specific fit for a narrower heel and overall slimmer fit.