NOVELTY - A mounting mat (20) for exhaust gas treatment device comprises: inorganic fibers; organic binder; antioxidant; and optionally an intumescent material. The mounting mat further comprises clay.    USE - As a mounting mat for exhaust gas treatment device selected from catalytic converter, diesel particulate trap; and as end cone insulation in exhaust gas treatment device (claimed). The mounting mats are also useful in a variety of applications such as conventional automotive catalytic converters for motorcycles and other small engine machines, and automotive preconverters; high temperature spacers, gaskets, and future generation automotive underbody catalytic converter systems; in diesel catalyst structures; and in any application requiring mat or gasket to exert holding pressure at room temperature and to maintain holding pressure at elevated temperature, such as during thermal cycling. The catalytic converters are useful in the chemical industry, and useful within exhaust or emission stacks, including those which contain fragile honeycomb type structures that need to be protectively mounted. The mounting mat material is also useful as passive fire protection, as a tire stop material, and for wrapping heat generating elements within fuel cells.    ADVANTAGE - The mounting mat is useful for mounting fragile catalyst support structure such as fragile ceramic monolith in exhaust gas treatment device selected from. The inclusion of antioxidant in mounting mat reduces negative expansion of the mat experienced at temperatures of less than or equal to 350 degrees C, and provides improved holding pressure performance i.e. resiliently holds fragile catalyst support structure, across a wide temperature range. The mounting mat is capable of maintaining a minimum holding pressure of ( greater than or equal to 10, preferably greater than or equal to 50) kPa, after undergoing 1000 mechanical cycles of a standard 1000 cycle gap expansion test conducted at a hot face temperature of about 300 degrees C with mat gap bulk density of 0.3-0.6 and 0.7-1.25 g/cm3 and percent gap expansion of 2%. Further, the use of a combination of antioxidant and clay leads to an increase in the overall resistance to shear strain as compared to mounting mat containing no antioxidant.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for the following:    (1) an exhaust gas treatment device (10) comprising: housing (12); fragile structure (18) resiliency mounted within housing; and the mounting mat disposed in gap between housing and fragile structure; and    (2) an end cone for exhaust gas treatment device comprising: outer metallic cone, inner metallic cone, and cone insulation comprising inorganic fibers, organic binder, antioxidant and optionally intumescent material, disposed between outer and inner metallic end cones; or outer metallic cone, and self-supporting cone insulation comprising inorganic fibers, organic binder, antioxidant and optionally intumescent material, disposed adjacent inner surface of outer metallic end cone.    DESCRIPTION OF DRAWING(S) - The figure shows a fragmentary view of exhaust gas treatment device including mounting mat.    Exhaust gas treatment device/catalytic converter (10)    Tubular housing (12)    Housing inlet (14)    Frangible structure/ceramic monolith (18)    Mounting mat (20)