lightweight support, responsive cushioning. the nike flex experience 3 boys' running shoe features a sandwich mesh upper with leather and synthetic leather overlays for breathability and durable support. a phylon midsole provides comfort, and flex grooves in the rubber outsole offer a smooth, efficient stride.. benefits. sandwich mesh upper with leather and synthetic leather overlays for breathability and durable support. phylon midsole for flexible, lightweight cushioning. rubber outsole with flex grooves for traction and flexibility.