The Sidi Mag-1 Boots feature an innovative internal brace system constructed from carbon fiber for the ultimate in support and light weight design. The Mag-1 Boots weigh in at 4.4 pounds each, or 17% less than the Vortice boots. An all new Micrometric Tecno 3 magnetic closure system makes adjustments quick and easy and the internal brace system provides ankle stability and flexibility. The rear upper is made in polyurethane and is assembled to the boot with two screws: one on the outside under the TECNO-3 Magnetic mechanism, the other on the inside which holds the micrometric adjuster strap. The screws support and block the internal support system which is made with carbon fiber beams, making up the frame of the boot. This system allows excellent flex movement front-to-back while being firm side-to-side. An all new Micrometric Tecno-3 magnetic closure mechanism is easy and quick to use as well as being highly adjustable and light in weight. The TECNO-3 Magnetic closures close the boot with an extremely resistant steel wire, that is hooked to the clip with the aid of a magnet. Sidi has created an incredibly solid boot with well-chosen design elements and materials to create a very lightweight, yet ultra-protective race boot system. Features: Arch and Achilles areas are covered with Sidi?s exclusive elastic textile and injection molded polyurethane comfort panels. Arch area utilizes two TPU bands next to the TECNO-3 Magnetic closures, for a maximum support and wrap of the arches. Asymmetric and shaped shock absorbing heel cup, smooth and flat inside for more adherence with the bike, with shock absorbing system in the back and outside. The shell and the shock absorbing system are replaceable through a screw and an interlocking system. Nylon inner sole with removable arch support pad. Replaceable external shin, heel and toe sliders. Nylon inner sole. Dual compound sole. High stress areas are double stitched. TPU shift pad. Perforated, Teflon treated nylon inner lining with Cambrelle lining in the toe area. Recessed screws used to attach replaceable parts so as to not damage bike. Toe slider made from nylon reinforced with fiberglass. Toe Slider features new air intake and alloy insert. Adjustable calf on the Sidi Mag-1 Boots can accommodate riders with up to an 15-inch calf diameter when measured 11.5-inches up from the bottom of the heel.