Alpinestars SP-X BOA Drystar Boots. Main upper constructed with a combination of advanced microfiber, knitted mesh and co-injected TPU with Lycra for the optimum blend of comfort, breathability and performance. Lateral side entry system incorporates BOA Speed Lace System technology for a quick, precise, and secure closure. Equipped with a Drystar® liner for proven all-weather performance, remaining waterproof while still being highly breathable. Rubber sole utilizes a special compound that provides textured grip and excellent absorption, and features an integrated support shank for an enhanced sole rigidity. Sports sole design incorporates a high flex inner structure (lasting insole) for superior walking comfort. TPU sliders are strategically positioned on the lateral toe-box and on the lateral calf for optimum flexion and protection.