I have no personal experience, but i have been told that the wrap traps in moisture and holds it against your manifold, exhaust, etc. and will accelerate oxidation/rust. Now i do not know how true that is and i have also been told that you can get a heat wrap sealant/glue that you can spray over the wrap that will seal it up and keep it from getting any moisture. Which is also something i am not certain about. Take this how you will as i have said this is just what i have heard and do not know to actually be true.