NIKE Women's Flex Run 2015 Running Shoe synthetic-and-mesh Synthetic sole Asymmetrical upper design for targeted ventilation and support. Breathe Tech construction on the lateral side upper fuses foam and mesh. Synthetic leather wraps the medial side upper for a secure fit. Lightweight Phylon foam in the midsole is pressure mapped for comfortable ride. Phylite midsole is durable enough to double as an outsole.