Abstract: A heat and chemically resistant sealing member particularly for an electrolytic cell of the diaphragm type in which the cell includes a cell can for containing a brine solution, a rigid cell base for supporting the can and anode members disposed within the can. The sealing member comprised of at least one vulcanized rubbery polymer provides a compressive seal between rigid members of the cell and is subjected to the heat within the cell. After long periods of exposure to this heat the sealing member is of a relatively flexible, resilient rubbery nature and has a relatively high resistance to compression set to thereby retain its sealing properties. The sealing member is preferably a flexible elastomeric sheet particularly useful for providing a seal and cover for the conductive base of the cell.