The objective of this work was to develop a numerical model allowing to predict the foaming process of a rubber matrix in injection molding conditions. This was achieved in two parts: the first one is a microscale model that describes the nucleation and subsequent growth of the bubble, with the latter being based on Amon and Denson’s work [1], which describes the growth of numerous cells in close proximity of one another. Each one of those cells is formed by a bubble enveloped by a spherical fluid shell that contains gas generated by a chemical reaction. As the dissolved gas diffuses towards the bubble, the pressure increases, which will induce its growth. The bubble grows up until the moment when no more gas is available. By applying the conservation of momentum, mass, and energy principles to this process, one can obtain a set of equations describing the evolution of the bubble radius, the pressure, and the concentration gradient inside the polymer. In addition to initial and boundary conditions (such as the initial gas concentration, bubble density, temperature, and pressure in the surrounding medium), different physical parameters need to be determined or estimated: diffusivity, Henry’s constant, surface tension of the fluid, and matrix’s viscosity, density and heat capacity. As the rubber is vulcanizing during the molding step, the viscosity increase due to the vulcanization was implemented into the model. An empirical model was used to introduce a state of cure dependency into the viscosity term. The state of cure evolution was predicted by means of a Kamal-Sourour autocatalytic kinetic model [2]. In addition, the coupling with the kinetic reaction generating the gas from a chemical foaming agent (OBSH) was also considered. The second part consists in coupling the microscale model with a macroscale simulation of the injection molding process, including the polymer flow into the cavity during the filling step and the evolution of its temperature throughout the molding step. This coupling was achieved by means of a commercial finite element simulation software: REM3D®. The bubble growth kinetics will be first described and discussed in view of the gas concentration evolution and the vulcanization kinetics. A parametric study will be conducted to determine first order parameters of the bubble growth process. Predictions of the bubble growth model will be compared with experimental data (foam density and bubble size distribution). The numerical coupling with the injection molding process will be discussed. Acknowledgements. This work was performed within the framework of the chair DEEP, between Hutchinson, ESPCI and MINES Paris - PSL. Hutchinson SA is acknowledged for its financial and technical support. This work is also supported by the French Minister of Research (ANRT). References. 1. M. Amon and D. Denson, Polym. Eng. Sci. 1984, 24, pp. 1026-1034. 2. M. R. Kamal. Polym. Eng. Sci. 1974, 14, pp. 231-239