DESIGN & TECHNOLOGY: Hard shell construction with lightweight & rugged outer shell Features MIPS(R) (Multi-Directional Impact Protection System) Technology for exceptional protection MIPS(R) Technology includes a interior foam liner, a Low Friction liner and an elastomeric attachment system that sits between Spherical Technology Ball-and-Socket design redirects impact away from brain with rotating outer liner Polartec(R) power grid bi-component knit construction for moisture-wickingcomfort In Form(TM) 2 Fit System creates a low-profile fit and stability system with 6cm of adustment Fidlock(R) one-handed magnetic buckle closure for s strong and secure locking force Stack Vent(TM) helps keeps goggles clear and fog free Thermostat(TM) Control Adjustable Venting lets you adjust airflow using a low-profile control button on outside of helmet Seamless compatibility with all Giro(R) goggles SIZING: We recommend you try helmets on before buying. Make sure the helmet fits with a little room when the fit system is loose, and sits low enough to protect your child's forehead without hindering vision. Once you've got the right size, you can adjust the fit.