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: X Small: 20.8 - 21.2" (53cm - 54cm) Small: 21.6" - 22" (55cm - 56cm) Medium: 22.4" - 22.8" (57cm - 58cm) Large: 22.8" - 23.2" (58cm - 59cm) X Large: 23.6" - 24.4" (60cm - 62cm) XX Large: 24.4" - 24.8" (62cm - 63cm)