i found exhaust material at a good speed-parts oriented auto parts store.. not one of the large franchises or chain stores.
This material came in a 12" wide x 24" roll, is a light grey/whiteish color, 0.03" thick and very stiff, almost brittle .. i think it's a ceramic fiber paper.
When it burns in a propane torch flame it smokes at first and you can smell the rubber (?) binder burning away.. But the material does not burn to ash .. the paper just glows red hot, turns black when it's cool and retains much of it's strength.