Allston bicycle helmet, known to be the most ventilated helmet in Bern, it is designed for those who are bothered by the helmet, or for professional users (such as couriers). Weighing only 340g, it can be considered the most airy helmet in the range with no less than 16 openings offering maximum breathability for cyclists. Its folding flip flop visor offers the necessary modulability for all weather conditions. Sizing guide : S : 52 to 55.5 cm M : 55.5 to 59 cm L : 59 to 62 cm It is made from a scratch-resistant ABS shell with EPS shock absorbing foam and BERN's exclusive ZipMold technology for high impact resistance. In order not to neglect comfort, a foam headband is clipped into the helmet's interior. An adjustment wheel is present to facilitate helmet adjustment.