The debonding process in a glassy polymer filled with glass beads during constant strain rate tensile loading has been analysed both theoretically and experimentally. A model which combines concepts of damage mechanics and the time dependence of interfacial strength has been proposed and compared with experimental results on glass bead-filled polystyrene. The stress-strain behaviour and the debonding could be modelled using a Bartenev-type relation for the destruction of the interfacial bond and by considering the gradual transformation on the initially well-bonded composite into foam. A good agreement between calculated and experimental data was achieved.