I have seen many posts saying that the kevlar fiber back is just a marketing ploy and serves no useful value. Kevlar is very scratch resistant and used in may products from tires to body armor to provide high strength and low weight. It is kinda like gorilla glass for the back of the RAZR and does not interfere with electronic signals like a metal or carbon fiber back. Because it is very thin it helps to reduce weight with the back being very flexible as shown in the Ifixit tear down video. It also is a very water and fire resistance material which may not be a big deal but definitely a plus. The soft fabric non-slippery feel of the back makes it easier to hold without slipping in the hand, especially with one-handed operation. There are a couple of scratch tests already on Youtube that I believe would have scratched a metal or plastic back. It makes me more comfortable to run it naked knowing that most of the back us protected by a thin layer of this strong material. Although I agree that there is marketing value in advertising the kevlar back I believe it is not merely a marketing gimmick and does serve a useful purpose.