An InfraRed Suppression System (IRSS) includes a double-walled exhaust duct and double walled septum. The double walled structure provides a flow path for secondary (non-exhaust gas) cooling air flow to slots along the surfaces exposed to exhaust gases. Exhaust gas flow past these slots draws cooling air across the duct and septum surfaces. This flow cools the surfaces close to the slots and mixes with exhaust gasses downstream to cool the exhaust plume. The septum in the shape of a helix rotating 360° fully blocks line-of-sight to the turbine exit from the aft of the aircraft. The exhaust duct is intended to be shrouded by an aerodynamic fairing which provides an aerodynamic contour which minimizes aerodynamic impact on the aircraft.