The capillary properties (wetting, infiltration) of the reactive Si/porous graphite system are studied by the sessile drop technique that enables the spreading and infiltration dynamics to be monitored in situ. The experiments are performed by varying the temperature, the type of graphite (porosity, grain size) and the vapour phase (inert gas or high vacuum). Further experiments are performed in order to quantify the influence of the exothermic reaction between Si and graphite on the temperature field close to the infiltration front. The effects of Si-graphite interactions on graphite mechanical integrity are also evidenced.