A helmet feature is composed of four parts: an AIRHOLE, a STRAP, a VISOR, and an earhole. An AIRHOLE is a small opening in the helmet that allows air to circulate, while a STRAP is used to secure the helmet to the head. A VISOR is a transparent shield that covers the face and eyes, and an earhole is an opening in the helmet that allows sound to enter. All of these features are important for providing protection and comfort when wearing a helmet.