Final answer:
Kevlar is the material commonly used in bulletproof vests due to its high strength-to-weight ratio and durability, making it also suitable for various applications such as combat helmets and protective gear.
Step-by-step explanation:
The material commonly used in bulletproof vests is Kevlar. Kevlar is a synthetic polymer developed by chemist Susan Kwolek and is known for its high tensile strength-to-weight ratio, being five times stronger than steel of the same weight. This remarkable strength makes Kevlar an ideal material for a range of applications, from personal protective equipment like bulletproof vests and combat helmets to various industrial and recreational products such as boat hulls, ropes, and sporting equipment. Additionally, the low thermal conductivity of Kevlar also makes it suitable for use in cryogenics.
While materials like boron, graphite, and aluminum have their own distinct properties and uses, Kevlar stands out for its protective capabilities. Unlike boron fibers, which are also very strong but much more costly, Kevlar offers a more economically viable solution for many applications that require high strength and durability.