Built with an aerospace shell design and materials, Troy Lee were able to get the D4 Composite helmet to 1050 grams without sacrificing any strength. MIPS (multi-directional impact protection system) is used to add an additional layer of safety in the event of a fall. For comfort, the D4 Comp routes cooling air through a front air intake system that flows through the polymer centre and power grid side mesh keeping your head cooler during the ride. X-static and XT2 anti-microbial/anti-odor padding keep the inside of the helmet a much nicer place to be. Size Guide: Medium = 22.4-22.8\" (57cm-58cm) Large = 22.8\"-23.2\" (58cm-59cm) X Large = 23.6\"-24.4\" (60cm-62cm) \"