A flexible and substantially crack resistant intumescent, non-intumescent, or hybrid mounting mat material for use in mounting fragile structures includes at least one intumescent, non-intumescent or hybrid layer containing inorganic fibers and reinforcing layer applied to the layer. Also provided is an exhaust gas treatment device including a housing, a fragile catalyst support structure mounted within the housing, and the crack resistant mounting mat disposed in a gap between the housing and the fragile catalyst support structure. Also disclosed are methods of making a mounting mat for an exhaust gas treatment device and for making an exhaust gas treatment device incorporating the mounting mat.