Disclosed is a mat or molded pre-form that may be used as a mounting mat to mount a fragile monolith within an outer housing of an exhaust gas treatment device, such as automotive catalytic converters and diesel particulate traps. The mat or pre-form may also be used as thermal insulation in the end cone regions of the exhaust gas treatment device. The mat and pre-form includes an inorganic microporous insulation component and a flexible fibrous material component. Exhaust gas treatment devices and methods for making exhaust gas treatment devices including the mat or pre-form are also disclosed.