The principal concept behind Nike Free is to replicate a barefoot feel through a siped outsole, with the deeply cut grooves allowing the sole to flex freely. Building off that original idea, along with new studies that reveal how the food expands and contracts on impact, the Nike Free RN Motion Flyknit takes that original technology even further. An auxetic, or splaying, midsole, spreads across two planes with a geometric tri-star form that's able to handle the massive changes in foot size -- approximately one size in length and two sizes in width -- that occur during the runner's stride. The new tooling, made with dual-injection technology using two foams fused with heat instead of glue, combines with Flyknit to deliver more cushioning than previous Free models. The upshot: the most natural ride yet. Stay tuned for release details.