The sandwich molding process consists of injecting sequentially a skin and core polymers. The thermomechanical model describing the flow of the two polymers into the mold cavity is based on the lubrication approximations. A transport equation characterizes the displacement of the interface between the two fluids. An experimental study has been performed in order to test the influence of processing parameters (viscosities, flow rates, etc.) on the interface location. Numerical simulations are in agreement with measurements.