[vettestr]

Most of the mufflers I have taken apart did have a fiberglass mat or something resembling it in addition to baffles. The material over time shrinks and the air between strands seems to disappear making it more dense so less effective or louder. I would bet gas would not do a darn thing as it would not get hot enough ??? No ideas here.

My exhaust builder uses stainless wool to build his muffler with a ceramic mat also part of his muffler. He told me cheaper materials can melt into BB like objects that rattle and blow out the pipes.