Abstract: A resistance heating coil is placed on a sieve like tray above a suction box, and a slip of ceramic fibers is placed in the suction box, so that a ceramic fiber layer builds up when suction is applied. Portions of the sieve like tray are closed in regions beneath the resistance heating coil by strips in such a manner that the impervious regions of the sieve like tray are narrower than the width dimensions of the heating coil so that the space inside the heating coil remains free of fiber material during the vacuum moulding operation. This allows the heater to be operated at a higher temperature without the risk of crystallization of the fibers.