To the naysayers on this thread I ask 1 simple ? Have you ever used exhaust wrap or are you simply repeating someone else's comments?
I installed header wrap on a set of nickel plated shorty headers on my 5.0 Mustang. It's been there for well over 10 yrs. and they have not rusted away. In terms of how well it works, I would characterize it as excellent. I had a Ford mechanic comment on how well it reduced the underhood temps when he was performing diagnostics. You can actually touch the wrap w/out burning your hand when the motor is fully warmed up. It allowed me to utilize a larger diameter primary header pipe and maintain/improve scavenging.
Sure it will retain H2O, but once your motor comes up to temp all humidity will evaporate. The only drawback that I'm aware of (at least on stainless) is that it can lead to cracking. Stainless is much better at heat retention and I wouldn't bother using it IF I had stainless headers. Sure coatings look cool and do the same job, but not as well UNLESS they are applied to both the inside and outside surfaces.
