Intumescent sheet material containing low density fillers

A low density flexible intumescent sheet useful for mounting diesel particulate filter monoliths comprising from about 10% to about 55% by weight of unexpanded vermiculite flakes having particle sizes of from about 0.1 mm to about 6 mm, from about 10% to about 50% by weight of inorganic fibrous material, from about 3% to about 30% by weight of binder and from about 10% to about 40% by weight of inorganic low density filler component, said sheet, having an average bulk density of from about 0.25 gm/cc to about 0.525 gm/cc, when packed about a ceramic catalytic converter core within a metal canister at a mount density of from about 0.40 gm/cc to about 0.68 gm/cc having a green push out force (as herein defined) against said core of at least 10 Newtons, said sheet upon exposure to heat from an engine exhaust being capable of undergoing thermal expansion to such an extent that said sheet in its expanded state has a hot push out force (as herein defined) against said core of at least 1700 Newtons.