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 : from 52 to 55.5 cm M : from 55.5 to 59 cm L : from 59 to 62 cm It is made from a scratch-resistant ABS shell with EPS shock absorbing foam and BERN's exclusive ZipMold technology, which provides high impact resistance and a foam headband is clipped to the inside of the helmet to ensure comfort. To ensure comfort, a foam headband is clipped to the inside of the helmet and an adjustment wheel is provided for easy helmet adjustment.