[ERA Chas]

That's a great tech article Bill posted about 303. Perfect explanation.
I have used it for two decades on tires and on my street cars, all black trim pieces.
Especially effective on the trim at base of windshields, black rocker panels and bumper top trim on station wagons. The key is removing the excess. It does work. The only area I have found in conflict with their explanation is that it will wash-down and streak when rained on or washed. But it does protect and keep things fresh-looking and pliable.