Some are oils (e.g., Meguiar's "trade secret oils" and the stuff in 3M IHG), and some others are forms of clay. The clays are so fine as to be functionally nonabrasive on automotive paint. I bet there are other forms of "fillers", but those are the ones that come to mind.
These ingredients get "stuck" or deposited in the crevices/pits/micro-fissures in the paint, literally filling them. That's why they don't do much of anything to improve the look of a (hard, non-porous) finish that's already truly perfect (i.e., smooth). E.g., whenever I used Meguiar's "pure polish" on perfectly polished Audi clear, I got *zero* improvement. There were no flaws for it to get caught it, it merely wiped on, and then wiped right *off* the hard, smooth surface without leaving anything behind to effect an improvement.
