Breathable Mesh: Cools & Dries Feet Dual Layers(Knit together): Keeps Feet Dry Y Heel: Improves Fit Anti-Slip Wedge: Helps prevent sock from slipping down into shoe Size Chart: Small = W 5-7 / M 3.5-5.5; Medium = W 7.5-9.5 / M 6-8; Large = W 10-12 / M 8.5-10.5 Drymax socks achieve the best fit because they were developed on special 3D foot shaped models which accurately represent the human foot as opposed to the 2D industry standard. The breathable mesh creates air flow between toes and top of foot, helping feet stay cooler. The MicroZap silver odor fighting technology in the Drymax Fibers actively fights odor, helping keep socks odor free.