Stretch-knit upper expands and contracts with your foot. U-shaped Max Air unit provides responsive cushioning. Flywire cables deliver secure lock down. 4-way stretch knit throughout the upper expands and contracts with your foot. It works with the partial bootie to deliver a secure feel. Injected Phylon (IP) midsole for lightweight cushioning and comfort. Articulated forefoot design works with the deep flex grooves for a smooth, natural range of motion through footstrike. Segments of solid rubber under the toe and heel enhance durability in these high wear zones.