The HUD-Y doesn&';t skimp on ventilation thanks to the two large vents and channels built into the foam that pulls air over the head. The feature that takes the helmet to the next level is the magnetically attached, USB rechargeable, rear LED light. The light provides a wide angle of visibility and has four different light modes, including Power Mode, Eco Mode, Blink Mode or Pulse Mode. In addition to classic color designs, there are also signal and a wide range of fashion forward options. For those that want to show up to their destination in style, there is no better option than the ABUS HUD-Y. Features Four-shell in-mould design for a durable connection to the outer shell with shock-absorbing helmet material (EPS) Height-adjustable Zoom Ace Urban fit system with ponytail compatibility for riders with longer hair Multi-position visor for excellent air circulation and protection from the sun. Wide-angle LED light with high power and magnetic attachment Depending on the mode, the light has a maximum luminosity of nine lumens. The four modes are Eco Mode, Power Mode and Blink Mode and pulsing LED light recharges quickly via micro USB. The color of the LED indicates when the charging process is finished ActiCage: Reinforcement of the helmet structure, which is integrated into the EPS hard foam of a helmet. The cage architecture creates space for large vents openings. FidLock magnetic buckle Laterally adjustable, non-slip TriVider strap system Size Guide Small - Head Circumference: 51-55cm Medium - Head Circumference: 52-58cm Large - Head Circumference: 57-61cm How to measure my size? Helmet sizes are based on head circumference. Measure your size by wrapping a measuring tape snugly around the widest possible circumference - from the most prominent part of the forehead (often 1-2 fingers above the eyebrow) around to the widest part of the back of your head. Measure 3 times, and take the largest number. Using the chart above, select your size.