What features should I look for in a bike helmet to make sure it’s comfortable and safe? 

Let’s begin with “safe” and work backwards. Until recently, testing by the Consumer Product Safety Commission was your best assurance that a helmet would help save your brain. And while that’s a good start, critics have noted that most helmets are designed to buffer linear acceleration only – preventing your skull from fracturing on impact. They don’t account for angular acceleration, which causes your brain to bounce around inside your skull. That’s important, says Dr Andrew McIntosh, a researcher at the University of New South Wales, Australia, because angular acceleration can cause concussions. At this point it’s unclear how much extra protection would be provided by a helmet designed to reduce angular impact, but why not look for one anyway? No matter which helmet you choose, the fit will affect both the comfort and safety, McIntosh says. You want it to be snug, and when you adjust the chin strap, you should not be able to slip more than two fingers between the strap and your chin.