Whether it's hard-charging trails or hammering hills, the 100% ALTEC is the rider's choice for an incredibly lightweight, ventilated and protective trail helmet. Featuring the Smartshock® Rotational Protection, the ALTEC's patented Smartshock® elastomers begin defusing rotational crash energy immediately upon impact. FEATURES Smartshock® Rotational Protective System (14 point). Multi-Density EPS foam injection molded with polycarbonate in size specific molds (XS/S, S/M and L/XL). Massive airflow with an impressive 15 ventilation ports. Expanded coverage while still lightweight. Integrated sunglass storage system. Multi-point adjustable visor designed for maximum vision and goggle stowage. Washable, moisture-wicking anti-microbial liner. Adjustable ratcheting fi tment system. Fidlock SNAP magnetic buckle (NEW for 2021). Size Guide table, th, td { border: 1px solid black; border-collapse: collapse; } th, td { padding: 15px; }  SIZE US SIZE EU LINER SPARE LINER LINER COMPATIBILITY XS/S 50 - 55 10MM 12MM XS/S Only S/M 55 - 59 10MM 12MM S/M Only L/XL 59 - 63 10MM 12MM L/XL Only