The Trian helmet is one of S-One's most popular skateboard helmets. All Trian helmets come with an extra set of pads in the opposite size. Smalls and Mediums are interchangeable and Large and X-Large helmets are interchangeable for a custom fit. Trian helmets fit people with narrower heads. The Trian helmet is a professional grade helmet with soft inner foam padding. It is NOT CPSC certified for bike usage. Sizing as follows: Small-19-20", Medium-21", Large-22", XL-23".