First is the Sidi Soft Instep 2 strap, linking the buckle tongue to the shoe does a great job of spreading out the pressure of the retention system so you don’t feel any restriction on your foot. The buckle has three elements to it. There’s the fast lever, the micro-adjust levers, and the release button. You can slide the tongue in, ratchet down quickly, carefully micro-adjust, then release. The Velcro straps actually have plastic teeth in the middle of them. They supplement the hook-and-loop closer system. The final element is the reinforced heel cup, which keeps the back of your foot firmly in the shoe no matter how hard you pull up.
The sole is their Millennium 5 shoe bottom. It’s a carbon-injected nylon. It’s stiffer than a nylon sole, but saves on the cost of a carbon sole. The cleat mounting system is the standard Look three-hole setup, with a fourth “memory eyelet” for folks installing Look cleats. The heel has a soft, replaceable heel pad.
The upper is a mix of nylon mesh and microfiber. The mesh is for keeping your feet cool, while the microfiber limits stretch, and is tough enough to keep going (and looking good) after a sliding crash.