Abstract: An improved exhaust port plug is provided for use in a baking furnace for the baking of anodes for use in an electrolytic reduction cell. The improved exhaust port plug comprises a cylindrical metal shell having a diameter approximating the diameter of the port, a cover member on the shell having a dimension exceeding the diameter of the port, a gasket means on the underside of the cover member surrounding the shell and adapted to sealingly engage an external portion of the furnace, a mat of packed ceramic fibers within the shell, and retaining means to retain the mat of ceramic fibers within the metal shell.