Also the stretch fabric around the calf, crotch, pits, and forearms, if they are just stretch material they will tear easily, they need to be kevlar reinforced, the only way to really tell is to look in them, if the inside has a grey hue to it then it usually is kevlar reinforced, if it is the same color as the outside then its just stretch material and a good tug and it will tear off at the stiching.Just to let you know...
Bovine Leather (2.5mm) will last about 28 seconds before it wears through - thats the leather you usually find in made-to-measure race suits.
Bangladeshi hide (1.4mm) will wear through in a 5.8 seconds - closer to off-the-peg suits.
Typical bike fabric sample will last about 2.1 seconds and jeans, well they take about 0.6 seconds to wear through.
Of course, in most protective clothing you'll probably have armour in the likely impact points, which adds considerably to the amount of abrasion they can take, but it gives you a rough idea of what your kit can take before giving up.
(Bovine leather however IS going to be the most expensive. Don't think because its leather you will survive better in a crash, it depends also on how good the quality and the craftsmanship is (seams etc)).