Header Wrap, what do you like

how do they retain moisture if they are always hot? I had some on a garaged car for 4 years and the headers faired fine. I used stainless pipe clamps on mine to secure them
Long ago I used the wrap but I didn’t have a garage to House the car. The headers rusted out of the daily driver.
The headers heat, I thought, would heat the wrap and boil the water out of the wrap. This is not the case and I can not explain why the wrap stayed moist/wet. Where ever the wrap was soaked, the worst rust happened.

The wrap was not painted to water proof/protect.