Troy Lee Designs D4 AS Composite HelmetAlways Evolving. Built with an aerospace shell design and materials, we were able to get the D4 Composite helmet to 1050 grams without sacrificing any strength. Mips C2 protection system is used to add an additional layer of safety in the event of a fall. For comfort, the D4 Composite routes cooling air through a front air intake system that flows through the polymer center and power grid side mesh keeping your head cooler during the ride. X static