The majority of stainless exhaust systems on the market are made from T-409 stainless steel. Every stainless exhaust kit we sell is T-409. After a few months or years; depending on road conditions and the environment your exhaust will eventually accumulate surface rust. The best thing you can do is occasionally clean it up with a scotch brite pad. The only way to prevent any sort of rust is purchasing a T-304 mirror finish exhaust system. These kits will typically cost you 2-3x more.