It's waterproof but I wouldn't rate it as a protective coating. Doesn't bond securely enough to the metal for that. It was sprayed on top of butyl/aluminum sound deadening mats and covered it with a foam/vinyl barrier that I sealed at all edges and openings with silicone and more foam and then carpet on top of that. That project was initally intended to be just herculiner, and then after reading about the noise and heat it kinda snowballed into an expensive sound deadening project that didn't even involve herc and had a poor ROI; it's tough to try and make a Jeep something it's not. :dunno: