Automotive companies in many countries are competitively promoting the enhancement of the fuel efficiency in order to correspond to the environmental regulation of global automotive markets. The most efficient manner to increase the fuel efficiency of auto-vehicles is the light weight design of an auto body using the non-steel light metals, plastic and composite material instead of the conventional steel. For the more, the efficient energy usage and control in the vehicle become important according to expanding the supplement of electrical vehicles. In order to minimize the energy loss inside the vehicle, polymer foam material is widely used in vehicle interior components. Especially, polypropylene foam is tried to apply for the air duct as the channel of the cold or hot air flow instead of solid type polypropylene. The air duct by polypropylene foam can make by the twin-sheet forming process, which consists of heating process of sheet(up to 150℃), compression process by upper and lower dies and vacuum forming process and cooling process. The product quality of the air duct is determined by the uniform thickness distribution and distortion amount of each part etc. In this paper, numerical analysis of the twin-sheet forming process is carried out in order to predict the product quality of the air duct considering the thermo-mechanical properties of polypropylene foam and non-linear behaviors. Keywords: Polypropylene foam, air duct, twin-sheet forming, Finite element analysis, thermo-mechanical properties