These days, more and more body armor manufacturers are starting to use Ultra High Molecular Weight Polyethylene (UHMWPE) to make body armor, which offers extremely lightweight protection, and lasts the longest time as well, however, it can be slightly more expensive than ceramic and steel body armor. Still, since you won’t have to replace it every five years or so, it is still better value for your money.
PE armor works by using the heat of the bullet, and melting around it, therefore, stopping penetration and deflected fragments as well.
On average, UHMWPE body armor plates can have a shelf life of up to 10 years, however, if the plate is shot, you should obviously replace it. That is the same for all kinds of hard body armor plates.
Lastly, another important thing to remember is that no matter which plates you are using, your plate carrier can also get damaged over time, especially if you are wearing your armor regularly, therefore, keep an eye out for any tears in the seams of your plate carrier as well.