of the insulator the insulator will swell to fill the space and still have an extra capacity to expand thus with high density retained the heat insulator will have a low thermal conductivity an excellent insulating performance and excellent resistance to vibration as illustrated in fig1 there is another advantage in that even when the dimensions of the inner or the outer cylinder change due to the temperature variations the insulator can correspondingly swell showing no great change in heat insulating performance several specific embodiments of the present invention will now be described in fig1 4 showing the engine manifold reactor exhaust pipe and muffler reference numeral 1 indicates the engine 2 indicates the manifold reactor in which co and hc among the harmful emissions from the engine 1 are burned and transformed into harmless co 2 and water and 3 indicates the exhaust pipe which carries the exhaust gas out of the exhaust port of the manifold reactor 2 to the muffler 4 in the engine 1 1e is the combustion chamber of the engine in which the gasoline and the air react with each other in an explosion which generates the exhaust gas when the exhaust valve 1a opens the.