A helmet is a form of protective gear worn on the head to protect it from injuries, a variation of the hat. The oldest use of helmets was by Ancient Greek soldiers, who wore thick leather or bronze helmets to protect the head from sword blows and arrows. In the 2000s, soldiers still wear helmets, now often made from Kevlar rather than metal, to protect the head from bullets and shell fragments.
In civilian life, helmets are used for recreational activities and sports (e.g., American football, ice hockey, cricket, and rock climbing); dangerous work activities (e.g., construction, mining, riot police); and transportation (e.g., Motorcycle helmets and bicycle helmets). Since the 1990s, most helmets are made from resin or plastic, which may be reinforced with fibers such as aramids.
Helmets were among the newest forms of combat protection, and are known to have been worn by Romans, throughout the Middle Ages, and up to the end of the 1600s by many combatants. At that time, they were purely military equipment, protecting the head from cutting blows with swords, flying arrows, and low-velocity musketry. Some helmets, in order to protect the neck as well, have a sort of extension made of leather strips called pteruges, particularly common in the Middle East.
They were initially constructed from leather, and then bronze and iron during the Bronze and Iron Ages, but soon came to be made entirely from forged steel in many societies after about 950A.D. Military use of helmets declined after 1670, and rifled firearms ended their use by foot soldiers after 1700. By the 18th century, cavalry units often wore steel body cuirasses, and frequently metal skull protectors under their hats, called "secrets".
The Napoleonic era saw ornate cavalry helmets reintroduced for cuirassiers and dragoons in some armies; they continued to be used by French forces during World War I as late as 1915, when they were replaced by the new French Adrian helmet. It was soon followed by the adoption of similar steel helmets by the other warring nations.
The Prussian spiked helmet, or Pickelhaube, offered almost no protection from the increased use of heavy artillery during World War I, and in 1916 was replaced by the German steel helmet, or Stahlhelm, and afterwards it was worn merely for tradition.World War I and its increased use of heavy artillery had renewed the need for steel helmets, which were quickly introduced by all the combatant nations for their foot soldiers. In the 20th century, such helmets offered protection for the head from shrapnel and spent, or glancing, bullets.
Today's militaries often use high-quality helmets made of ballistic materials such as Kevlar, which have excellent bullet and fragmentation stopping power. Some helmets also have good non-ballistic protective qualities, to protect the wearer from non-ballistic injuries, such as concussive shockwaves from explosions, motor vehicle accidents, or falls. Military helmets can be worn with radio earmuffs, and other equipment such as night vision goggles, can be added. Military helmets are often worn with a removable cotton-polyester helmet cover, which allows the user to change the pattern of the camouflage (e.g., from dark green forest camouflage to tan-coloured desert camouflage).
Despite various designs and requirements, all helmets attempt to protect the user's head through a mechanical energy-absorption process. Therefore, their structure and protective capacity are altered in high-energy impacts. Beside their energy-absorption capability, their volume and weight are also important issues, since higher volume and weight increase the injury risk for the user's head and neck. Anatomical helmets adapted to the inner head structure were invented by neurosurgeons at the end of the 20th century.
Helmets used for different purposes have different designs. For example, a bicycle helmet would chiefly need to protect against blunt impact forces from the wearer's head striking the road or a car hood. A helmet designed for rock climbing, however, would need to protect against objects (e.g. small rocks and climbing equipment) such as an ice axe falling from above. Practical concerns also dictate helmet design: a bicycling helmet would preferably be aerodynamic in shape and probably well ventilated, while a rock climbing helmet would be lightweight and with a minimum of bulk so that it would not interfere with climbing.
Some helmets have other protective elements attached to them, such as a face visors or goggles or a face cage, and ear plugs and other forms of protective headgear, and a communications system. Football, hockey and lacrosse helmets usually have an integrated face protector (face cage) made from metal.
Furthermore, it became common to use a helmet (and/or some other headgear, e.g. a crown or coronet) as part of the coat of arms, above the shield, a practice maintained long after its use in reality was ended by military technology and the demise of jousting. In some systems, the rank of the bearer was reflected in the model of the emblematic helmet, e.g. the metal and the number of bars in the visor, as in France. Either way, the rank can be reflected by a coronet or wreath placed on the helmet (often instead of directly above the shield).
The heraldic convention in the United Kingdom is as follows: