NIKE Flex 2013 RN Running Shoes Synthetic *** UPDATED *** Full Inner Sleeve Construction - Wraps around the entire foot for a snug, comfortable fit and feel. ** UPDATED ** Lightweight Sandwich Mesh and Midfoot Overlay - For breathability and comfort. *** NEW *** Phylon Core - Features soft, yet resilient foam for a lightweight, comfortable ride. Full Length Flex Grooves - For enhanced flexibility and a smooth, efficient stride. Fused Phylite Midsole and Outsole - This ultra-lightweight material provide an extremely smooth and resilient ride giving you a comfortable running experience.