the ammount of engines ive seen been fire damadged by wrapped exhausts could fill a book, exposed they can get contaminated by oil, desiel, petrol,......... soaks into wrap............ nice hot exhaust and bingo a fire, only 2 things id put on mild steel exhausts is, 1 vht paint.....2 a sprayed ceramic coating but 2 is going a bit overboard as is expensive, but if you want to thrash your bike then hold one of the headers then ceramic coatings the way to go...........................