The H and N "high speed" copper plated bullets have a thin coating of some sort of plastic material which I assume is a polymer.
These are good to 2400fps, depending on calibre. They certainly stop any fouling from the copper plating. I assume the polymer coated lead bullets have a thicker polymer coating over the lead base.
Should not get any leading from a well fitting lubed lead bullet....an expert will be along in a moment...
amc577