Giro Slingshot Snow Helmet Hard shell over EPS foam liner In Form Fit System: Makes it easy to dial in a custom fit. An ergo-friendly dial at the base provides adjustment and enhanced stability, while vertical tuning accommodates different goggles and head shapes for a custom fit, free of gap 4 cool vents Compliance: ASTM 2040/CE EN1077 Extra Small/Small: 49-52 cm