Bump, color, ambience, all have an effect. Yet the 2 I focus more on is specularity and belive it or not metalicity, it tends to spread the specularity over the mat more evenly. More often I use sand/bump with increased in number size(decreased in size) for the bump, yet there are some fantastic leather mats out there. Grainy Bump, subtle Specularity. If you check my gallery you'll see a few styles of leather look. Good luck, hope to see what you come up with. ICM