coating isnt mandatory and does nothing for performance (its been proven) but if you dont coat them theyll look butt ugly in minutes (mine did). Also,if you coat them, the headers will cool down much faster after you turn car off than if they werent.One more thing,according to a test they did on one of my chevy magazines,the headers averaged about 215 degrees at idle and 266 or so on the highway (coated) and a bit over 500 at idle uncooated with the highway temps somewhere in the mid 500's but again,no power difference,actually a tiny drop in HP and TQ