7idp Limited Edition Project 21 Pro Helmet Advanced Protection Features Whether you're cruising the trails or shredding the singletrack, you should be wearing a helmet. The 7idp Limited Edition Project 21 Pro Helmet combines massive airflow with the coverage demanded by increasingly technical bike parks, all-mountain, and enduro trails. This airflow gives a cooling effect to keep you comfortable whilst concentrating on the trail ahead. Like its full-face sibling, the Project 21 uses Energy Reduction Technology (ERT). This patented 4mm layer of lightweight polymer material dissipates both linear and rotational impact energy. Unlike other systems, ERT responds instantly even at low-impact levels commonly seen in riding. In the helmet foam, there is additional hidden protection: Cone Head technology acts as a crumple zone, dissipating energy laterally. The dual-material, dual-density foam reduces the likelihood (or severity) of concussion. The Project 21 also uses our CRV (Crash Release Visor) system to make sure rotational forces are reduced on impact. Features Energy Reduction Technology is a 4mm layer of lightweight polymer material that dissipates both linear and rotational impact energy Cone Head technology acts as a crumple zone, dissipating energy laterally AGION Anti-Microbial fabric keeps everything fresh SPECIFICATIONSCore Material ERTClosure system7idp Rear Dial Adjuster Safety Certifications CE, CPSC, AS Standards Intended Use Mountain Bike Weight402g (M/L)Sizing Size Extra Small/Small Medium/Large XL/XXLHead circumference (in)52 - 55cm56 - 59cm60 - 63cm | 7Idp | Limited Edition Project 21 Pro Helmet Men's | Size Extra Small/small In Splatter