Until the Umbrella Chronicles, the material of what Nemesis and Mr. X wore was never revealed properly. In RE2 and RE3, they just appeared as trench coats and customized leather overcoats that bullets could penetrate and still draw blood, but in UC and DSC, they are displayed as being composed of materials that made bullets ricochet.
Now, what lightweight, flexible, weaved, clothes like fabric can make bullets ricochet as if they were composed of metal? I have seen it in certain science fiction films.