I don't think you can use steel wool all the way through for carbon cans as it'll transfer too much heat to the outer shell. I think this is why you need the fibreglass matting.
tony h is an exhaust specialist from the car side of things so could clarify things for us.
I was looking at ordering the matting from here as mine need doing soon.
http://www.aa16.co.uk/a16exhaustparts.htm £18 for 2 cans worth can't be bad.
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