Helmets consist of a hard plastic shell, foam padding with liner, and a steel cage. The majority of modern helmets offer tool-free size adjustment (length-wise) as well as via the chin and ear straps.
The key to look for when selecting a helmet is proper fit. Helmets should fit snugly over the head with little wiggle room. The player should not be able to slide the helmet down past the eyes without first loosening it. If the helmet doesn't fit properly, even after adjustment, it’s best to move on to a helmet that does.
Other traits to keep in mind are how protective the helmet is, how comfortable it is and how easily the size can be adjusted.