Helmet is a kind of equipment with unusual ability to protect the head, which is usually used in military training, combat, people's transportation and industrial production.
It is mostly semicircular and mainly consists of three parts: shell, lining and suspension device. Ancient helmets were mainly made of leather, cotton cloth, linen and metal, and recently they were also made of resin or plastic.
Modern helmet is mainly composed of helmet shell, lining and suspension system. Due to the different requirements of various activities, the structure and style of helmets are also diverse.
Usually, the shell of helmet is made of high-strength materials, such as metal, engineering plastics, Kevlar fiber and so on. , most of the impact force is absorbed through its deformation; The lining material has the functions of absorbing sweat, keeping warm and damping, while military helmets often have the functions of further slowing down the impact force and preventing the head from being injured by shell fragments. The suspension system is the part between the shell and the lining, which can usually be adjusted to meet the differences of different wearers' heads.
Some special-purpose helmets are also equipped with headphones and microphones, as well as sockets for installing additional equipment such as cameras and lighting flashlights.