Nike Dual Fusion ST 2 Running Shoes Breathable mesh upper - for breathability and a comfortable fit Internal Midfoot Strap - Runs from the midsole up to the laces for a snug, secure fit. Dual Density Phylon Foam - with soft foam in the center and firm foam at the perimeter for Flex Grooves - at the midsole and outsole for enhanced flexibility and natural range of mo Inner Sleeve - for a soft, comfortable fit.