Do Kevlar bulletproof vests expire? The answer is, YES, they certainly do. Most police forces in the US replace their Kevlar bulletproof vests every five years. Part of the protection that Kevlar provides is the weave of the fabric. A spinning bullet interrupts the weave, causing the force to be spread over a larger area. Over a period of years the fibers in woven Kevlar fabric start to separate, reducing the ballistic protection provided by the vest.
A great use for old Kevlar bulletproof vests is to add armor to your vehicle. A few used vests on the floor of your car, and on or under the seats will give you some protection against IEDs. Not perfect, but better than nothing!