A mounting mat for an exhaust gas treatment device, includes at least one layer comprising inorganic fibers and a heater in thermal communication with the layer. Also disclose is an exhaust gas treatment device comprising an outer housing, a fragile structure located in the housing and the mounting mat located between the housing and the fragile structure. A method is further disclosed for maintaining and/or increasing the temperature of a substrate of an exhaust gas treatment device comprising providing the mounting mat and transferring heat from the heater to the mounting mat in order to maintain and/or increase the temperature of the substrate and/or the exhaust gas treatment device during the battery mode of a hybrid gas/electric vehicle.