Abstract: Disclosed is a vehicle exhaust system containing a three-way catalytic converter. An insulated flexible duct connects the outlet of the engine exhaust manifold with the inlet of the three-way catalytic converter to retain the exhaust engine gases at a temperature greater than the ignition temperature of the three-way catalyst in the catalytic converter. The insulated flexible duct is preferably made of an inner flexible metal conduit surrounded by fibrous insulation which in turn is surrounded on the outside by a second flexible metal conduit. The system is economical, contains no active elements which would require maintenance or could get out of order, is adaptable to motor vehicles of all types (especially automobiles, light trucks and vans) including those powered by either gasoline and diesel engines and entirely eliminates the need for expensive and complicated light-off catalysts in the system.