I have not had any problems with my duster. I only let about 1/2 inch of the bottom of strands touch my paint. I NEVER rub the duster over the surface, I very lightly glide the duster over the surface.
I know how the scratches occur though. I have see some people at car shows actually using them like scrub brushes and trying to remove dirt from the finish, needless to say Scratch City!!
I agree with Brad`s logic, if used properly they are a great tool, but if used improperly, watch out!!
Bookmarks