SmartWool's PhD Running Ultra Light Low Cut Sock earned its degree in technical performance with a minor in the utmost comfort. Indestructawool technology uses merino wool for ultralight temperature regulation, natural odor-resistance, and long-lasting durability. SmartWool's 4 Degree elite fit system uses elastic bands at the ankle, upper instep, lower instep, and arch for greater stretch and recovery. This smart sock also features a virtually seamless toe and mesh ventilation zones for extra comfort.