Helmet is a protective device for the head. It is a cap worn by soldiers during training and combat, and an essential tool in transportation. It is usually semi-circular in shape and consists mainly of a shell, a lining, and a suspension system. The shell is made from special steel, fiberglass, reinforced plastic, leather, nylon, and other materials to protect the head from bullet heads, fragments, and other impacts. In ancient China, it was referred to as armor for the head, helmet, or headgear.
Modern helmets are primarily composed of a shell, lining, and suspension system. Due to the varying requirements for different activities, there are many structures and designs for helmets.
Generally, the helmet shell is made of high-strength materials such as metal, engineering plastics, Kevlar fibers, etc., which absorb most of the impact force through deformation. The lining material has sweat-absorbing, warm-keeping, and shock-absorbing properties. The helmet also often includes functions to further reduce impact forces and prevent shell fragments from injuring the head. The suspension system is the part between the shell and the lining and can usually be adjusted to fit different head shapes.
