Abstract: A device for plugging the taphole in reactors for metallurgical processes in which the plug includes: a solid element, made of refractory material, which expands in a substantially cylindrical head having a diameter greater than that of the tap-hole, and applied to the solid element, and O-ring packing made of a material consisting essentially of a mixture of a refractory material in powder form and of a binder, said material being cold coherent, plastically deformable for increasing values of the temperature within the limits of the thermal interval within which the mixture sets, and becoming indeformable for values of the temperature higher than the said thermal setting interval, but lower than the operating temperature of the reactor, after a period of exposure to the operative conditions longer than the time necessary for installing the plug.