If used incorrectly, a clay bar will scratch your paint. As long as you are continuously folding the bar to create new, clean surfaces you should be good to go. Also, if you ever drop the clay on the ground make sure the next thing it touches is a trash can. After hitting the ground, the clay bar will have some pretty nasty stuff on it and should not ever be used on a vehicle again. Anything that a clay bar leaves after proper use, which is usually nothing, should be able to be corrected by a very mild polish.