Thermally insulating septums are located internally within the cells of an acoustic honeycomb to regulate heat flow into the acoustic structure. The internally located insulating septums protect the honeycomb and acoustic septums located within the honeycomb cells from heat damage that might otherwise be caused by a heat source, such as the hot section of a jet engine. The internal thermal regulators are useful in combination with heat blankets or other thermal insulating structures to provide a reduction in size and/or weight of the insulating structure while still providing the same overall degree of thermal insulation for the acoustic honeycomb.