rock wool VS buying new packing

So a couple weeks ago I had a major failure with my pipe. I had to fab one up to hold me over till I can buy a new one. The question I have is has anyone used rock wool to repack their muffler? I don't think it will flow as good as the woven fiberglass that is in it originally, but it does seem to breath well to me?
Any thoughts?
-B

The fmf general packing i used was quite soft...didnt think it was fiberglass. As well the old stuff didnt seem like fiberglass either.
Anywho, I dont know what it was...I just wouldnt have guessed fiberglass.
And the only rockwool i'm familiar with is used in hydroponics or insulation...and you wouldnt want to use the stuff i've seen for packing.
The general fmf 4 stroke packing was cheap and worked well for me.
...if that helps.