Injection molding of polyurethane foam involves several steps. First isocyanate and polyol are mixed. The mixture contains also water which reacts with isocyanate giving CO2 and creating the foam. Then the mixture is injected at around 30 °C in the mold which is heated around 50 °C. It fills typically around 10 % of the cavity volume. When the gas creation reaction starts, the expansion of the foam leads to the full cavity filling. The curing reaction leads to the solidification of the foam. The kinetics of the two reaction must be precisely tuned so that curing does not occur too early, preventing the foam to expand, or too late, which can lead to foam collapse. For the numerical simulation of the foam expansion and mold filling, we used the software REM3D. It is based on a 3D finite element resolution of the compressible flow equations, of the energy equation which includes the enthalpy of the reactions, and of the reactions kinetics equations. The material data have been determined using a Foamat device. The computation gives the evolution of the flow front position, temperature, pressure and foam density. A center gated square mold with different thicknesses has been instrumented with pressure and temperature transducers. The latter are located at specific positions in the thickness of the cavity, allowing to monitor the arrival of the foam on the transducers and the temperature increase due to the chemical reactions. The density of the foam has been determined at different positions, the cell microstructure has been observed by SEM and cell size quantified by image analysis. Temperature and density are compared with the numerical results and the agreement is correct.