As described on Zapppos- "The HFS runs small. We recommend choosing 1/2 size larger than your usual size. A new lightweight, breathable mesh upper, a new tire tread-inspired sole, a silky moisture wicking lining made with ""37.5"" material, protected tension straps... put all of that together for your new favorite road running shoe, the Xero Shoes™ HFS. Vegan-friendly materials. Natural FIT - a wide toe box lets your toes spread, splay, relax, and function naturally. Flexible enough to let your feet bend, move, and flex the way, well, that feet are supposed to. You can remove the 2mm insole, for a closer-to-barefoot experience that lets you Feel The World®.Light weight - so light, in fact, you could forget you have them on. Huarache-inspired design - the adjustable instep and midfoot straps are not just eye-catching but functional, giving you a secure and comfortable fit. EVA footbed. The "XERO-drop design (non-elevated heel) allows for proper posture, and it's built low to the ground for balance and agility. Natural FEEL - the HFS has a 5.5mm FeelTrue® rubber sole to give you the right combination of protection plus ground-feedback, so your brain knows how to move your body optimally. Polyester upper and lining. Synthetic insole. Rubber outsole.