Compact, Cool and Durable. Authentic mountain biking performance and style. First and foremost, a mountain bike helmet should be comfortable and durable. The Phase is true to the core; light, cool and durable enough to handle even the most daunting climbs and rock-strewn ribbons of singletrack. With the easy fit and adjustability of Acu Dial 2 and the comfort of Super Fit sizing, it’s a top performer for riders looking for a low-profile helmet at a great price.