SIDI Astro Boots The Sidi Nitro Boots are now known as the Sidi Astro! All the same great features with a new name. Features Internal thermoplastic resin ankle ball protection cups. Nylon inner sole with removable arch support pad. 1.7mm thick Technomicro is used as a base material. Lined with Teflon mesh on the ankle, Cambrelle on the toe and soft mesh on the tongue and gaiter area. Partially vented upper. Double stitched in all high stress areas. Sidis own Tecno 3 wire entry and closure system. Velcro strap above the instep area. Toe shift pad. Internal ankle padding. Durable high grip sole. Perforated details to improve ventilation. Internal shock absorbing heel cup. Reflective points above the heel.