I have been a law enforcement officer AND a body armor sales rep and I believe the problem is with the NIJ (The National Institutes of Justice) which is the organization that regulates body armor standards for vests sold to law enforcement in the US. The NIJ's "backface deformation" standard is the culprit. Basically, this standard means that a vest must not only stop a bullet, it must also not allow a "dent" over a certain size to be made in the testing media the vest is covering. The testing media is modeling clay. The problem is that a vest may stop a certain bullet with say, nine layers of material (kevlar, twaron, spectra, etc.) but it must be more than twice as thick to avoid making too big a dent in the clay. This results in a vest that is much heavier, bulkier, and uncomfortable than what is really needed to do the job. The NIJ's belief is that a dent over the size they say would result in the officer being incapacitated by the impact of the bullet. A lot of testing and real-life experience disputes this claim. Besides that, if the vest is too heavy, hot, or bulky the officer WON'T BE WEARING IT! The company I worked for sold armor all over the world. Vests (and other items) that didn't have to meet the NIJ standards, just the realistic standard of stopping bullets, and we had a lot a shootings survived by people the NIJ would have us believe should be dirt-napping.
The NIJ standard isn't based on good science. Modeling clay became the media of choice because...it's what they had lying around when they formulated the test. I believe that they have missed the point of body armor.
