Abstract: A hot gas seal for a conduits penetrating the wall(s) of a vessel such as a heat recovery steam generator unit. The seal will permit lateral movement greater than 2 inches (typically 2? to 10?) and unlimited axial movement without seal degradation and failure. The instant seal has a life expectancy of at least ten years. The seal includes three serially-arranged, independent insulation segments or pillows. The pillow adjacent the vessel casing and the center pillow employ metal sheets to sandwich insulation therebetween. The center pillow travels laterally with the conduit. The third or outer pillow terminates in a split seal ring having containment structure attached thereto.