What is this?: Cleaning Techno Estoril Exhaust (3 replies)

So took apart the second part of my exhaust today to hopefully clean it because i got it used and saw this foam or buildup of some sort and was wondering if I should remove it or keep it also there is like a steel wool material in it and was wondering if that was correct too, the foam or buildup or whatever it is is falling apart and so I put it back together before it all fell off was wonder what I should do with it of its build of of carbon or some sort of foam .

Thanks!

thewhistleblower