Protec have been making these helmets for years and their design is a timeless one at that. It features a multi-impact two stage liner, abs shell, stainless steel rivets, and soft tubular webbing. Sizing: Small = head circumference of 20.5in. - 22.5in. Medium = head circumference of 21.5in. - 23.5in. Large = head circumference of 22.5in. - 24.5in. Large = head circumference of 23.5in. - 25.5in.