The Nike Free outsole has laser-siped flex grooves, which release stiffness in the foam and allow it to move as naturally as the foot does.

It's not just the minimal design and breathable upper materials—Nike Free is shaped to the anatomy of the foot, so it fits like a second skin and feels like a natural extension of your body.

From top to bottom, flexible materials make it easy for the foot to move every way it needs to.

Tobie Hatfield, Athlete Innovation Director, and Eric Avar, VP of Innovation, conducted an exhaustive series of measurements to learn how the bare foot behaved while running. It was one of the first studies of its kind, and it gave them the data they needed to officially begin design on the first Nike Free.

Nike Free hits the same barefoot benchmarks first measured in the lab: balanced heel-to-toe pressure gradients, a 33-degree toe-off angle and a more neutral pronation pattern.

Once the study of barefoot running was complete, the team got started on the initial designs. The mission was clear: Set the 52 muscles of the feet free.

Nike Free resembles the pressure profile of the bare foot much more closely than traditional footwear.

Nike Free always helps enhance your body's natural motion, but the barefoot-like running experiences vary from shoe to shoe. These variances are graded on the Free Scale. The lower the number, the more barefoot-like the shoe.