UV light, High Heat, Moisture will degrade Plates, Soft aramid fiber armor over time. If you use it sparingly and have it stored in a cool dry place (kit bag, toughbox etc.) you're Good 2 Go. As BoilerUp stated expiration dates for the manufacturer's way of "covering their assets". I recently tested a 20 year old unused SAPI cut LEVEL III kevlar soft armor of which I have 3 sets of. It withstood the 9mm, 44, and 45 I shot it with.