This is a true racing flat, light and flexible to the extreme. The lower heel lift and lighter midsole greatly enhance flexibility and give the runner a real feel for the road. The blown rubber Vibram® outersole and fully slip-lasted construction helps minimize the shoe’s weight. One word of caution, however. This is a minimal shoe and is not intended for someone with bio-mechanical problems, nor for use as a day-to-day trainer. It is ideal for runners fixated on speed and their next PR.