Sidi ST Air Boots The patented and trademarked Vertebra System protects the riders Achilles tendon. Thermoplastic resin ankle protection. Bolt on (no Velcro!) replaceable, adjustable and aerodynamic nylon scuff pads on the toe. Composite inner sole. Removable arch support. Nylon shin deflector plate. Perforated Lorica outer construction. Double stitched in all high stress areas. All bolt on parts are replaceable. An elastic panel adjacent to the entry zipper allows a bind free zip and improved fit. Dual compound sole. DuPont polymer toe shift pad. Perforated Teflon treated nylon lining. Replaceable shock absorbing heel cup. Padded Achilles area. External Ankle Support Braces with Closable air vents Cam-lock buckle system.