over time?  is there a reason that police departments trade in their vests?  should someone be wary of buying vests that are over a certain age?  are there tests that have shown whether it makes any difference?

thanks

dunno...but, internet experts have told me it gets stronger by shooting at it.

I was told by a company rep that moisture and ultra violet rays break down kevlar. He also stated that the reccomended life span is very subjective. His advice was to keep it out of direct sunlight(easy) and to try to avoid moisture(Not easy, sweat).

I've got a friend who is a LEO supplier: The literature he has suggest replacing vests every one to three years depending on locale. Soft Armor Vests used in Hot, humid areas and/or with high alkaline backgrounds (Think beachfront), should be replaced every year.

Hard armor vests hold up better because the resin used protects it from contamination and breakdown.

I have another friend in the aerospace industry who commented that the East-Bloc ripoff of kevlar using in their aircraft was superior to the western stuff because it was more water resistant, but this was over 10 years ago, so things may have changed since then.

Kevlar is a woven fabric,  it'll wear just like any other fabric over time.  Dirt, sweat, folding and other abuse will weaken the fibers.  We replace ours every three years, or whenever it gets contaminated by chemicals.  (diesel, oil etc)

IMHO it doesnt matter. Ive shot ten year old vests that have been worn in Arizona summers and they worked like they were brand new. My theory is that it's the vest companies scam to keep making their money. I would have no problems wearing an old vest. I like getting a new one (dept paid 4)every five years because they keep getting thinner and lighter. I guess its up to the person wearing it to make the final decision on how they feel about it.