“I’ve heard that you can stop a 9mm with a lot of layers of clothing.”
You may have heard that, but it’s bullshit.
That one guy and his girlfriend had heard a phone book would stop a .45!
“It’d take a whole lot of silk to stop a 9mm. Denim and leather however has been found by FBI studies to stop 9mm bullets or at least reduce the velocity enough that lethal penetration is impossible. A good thick winter coat is almost a bullet proof jacket against a low end 9mm.”
And here is more: https://www.m4carbine.net/archive/index.php/t-129949.html
I’ve also heard that some windshields will deflect a 9mm round. This sort of thing is why I almost didn’t go 9mm. Almost. :)