Everyone makes some sort of clay bar product (this one is the Quik Clay from Meguiar's), and they're great for removing the surface imperfections you can feel with your hands. To use the bar, wash the car first, then lubricate the surface with an instant detailer type of product before rubbing the bar across the paint. You'll be able to actually hear the bar picking up gunk. When once side of the bar gets dirty, fold it on itself and knead it to bring up a clean surface. A bar this size should do a small car four times before it needs replacing. But do replace it, otherwise when the bar gets saturated with contaminants, they'll stay on the bar's surface and scratch the car.