The US Army, Marine Corps, and Navy typically use either full or half plate carrier systems in their armor systems. Hard armor plates, such as the MRAP (medium-army plate) and the LHP (light-army plate) are much heavier and are used for heavier armor application. Additionally, there are other types of armor that have been in service for decades, including soft armor for tactical vests and packs. In recent years, new materials such as the polymides used in Q-switched polyurethane soft armor have become available to the US military and contractors.
Soft armor made from high-density UHMWPE soft armor isn’t too thick nor too lightweight, yet it is very flexible and very light. But do not let the name mislead you, soft armor isn’t just capable of proving effective protection against firearms and ballistic fragmentation, though it can. In fact, it has the potential to become a good secondary or primary defense against other projectiles, depending on where it is used. Polyethylene is a fantastic material that offers many advantages over conventional materials, including its weight, dimensional stability, chemical and elastic properties, and overall impact and wear resistance. The high degree of flexibility offered by polyethylene makes it a naturally occurring product, but it can be manipulated to be shaped as desired. Also check: https://acelinkarmor.com/armor-plates/
As an example, standard sheet metal, including the M.A.S.S. jackets and plate carrier shirts used by the Marines, are primarily made from a medium-density fiberglass which is not only lightweight, but has a low impact and wear resistance, while having a high tensile strength. The problem with using standard sheet metal in protective applications is that it is usually rigid, making it difficult to bend or twist into a design that would be appropriate for its intended application, or even just to make it more lightweight. Soft armor, on the other hand, can be shaped into a pre-designed form, often with a hand-screwing process, which makes it more flexible and useful in a wide range of applications.