"The S-ONE Lifer Helmet is designed to fit low on the head like a traditional soft foam skateboard helmet. This helmet is a break through design combining the added safety of a CPSC certified helmet with the comfort of a soft foam helmet. We designed the Lifer Helmet specifically for Skateboarding, Roller Derby and Bicycling. The Lifer has an old school look with the traditional circular air vents." S: 21" - M: 21.5" - L: 22" - XL: 22.5" - XXL: 23" - XXXL: 23.5"