Specially formulated EPS Fusion Foam, Deep Fit Design Certified Multi-Impact (ASTM), Certified High Impact (CPSC) 5x More Protective Than Regular Skate Helmets To determine proper size, measure around head with a soft tape measure or string; each helmet comes with bonus sizing liners to size one step up and down Recommended for ages 5+ The S1 Lifer Helmet is one of the best fitting and safest helmets for Biking, Skateboarding, Longboarding, and Roller Derby. The Lifer Helmet uses a specially formulated EPS Fusion Foam which allows it to protect your head from multiple low force impacts as well as high impacts. The Lifer Helmet is a Certified "multi-impact" helmet and is up to 5x more protective than the soft foam non-certified helmets. The Lifer helmet is a break through design combining the added safety of an ASTM certified helmet with the comfort and fit of a non certified helmet. The S1 Lifer Helmet is the best fitting High impact and Multiple Impact helmet on the market.