Aramid, also known as Kevlar was developed in the late 1960s. It is a new high-tech synthetic fiber with strong high-temperature resistance, great anticorrosion, light weight and great strength. Thus Kevlar helmet is the mainstream equipment in the US Army and European army. However, Kevlar helmet also have shortcomings: vulnerable to ultraviolet light and easy to hydrolyze. It's not suitable to use or store in the environment with strong ultraviolet light and high humidity for a long time. Besides, the increase of the usage of Kevlar has pushed up the price of Kevlar's raw materials and then the price of Kevlar helmets.