Breathability. The Flyknit lets in a lot of air and my feet felt as cool as possible given the hot summer weather. The breathability is right in line with similar Flyknit models so it translates well to running.

The Nike Zoom Fly Flyknit running shoes are definitely true to size and I'd only recommend sizing up maybe half a size, if at all. It does depend how thick and padded your running socks are.

Nike Flyknit technology uses high-strength fibres to create lightweight uppers with targeted areas of support, stretch and breathability.

Though you can wear socks with the Nike Free Flyknit, the intent is that you don't. The upper has been engineered to conform to your foot and feel like a sock.