The potential application of geofoam in reducing the dynamic earth forces on flexible cantilever earth retaining walls was investigated through small-scale physical model tests. Tests were carried out using a state-of-the-art laminar container and a uniaxial shaking table. Deformable geofoam panels of low stiffness made from expanded polystyrene (EPS) and extruded polystyrene (XPS) geofoam were utilized as compressible inclusions in the present study. The dynamic stress-strain properties of these geomaterials are discussed based on results from laboratory cyclic triaxial tests. Lateral dynamic earth pressures and wall displacements at different elevations, within the backfill were monitored during the application of various base excitations. The test results revealed that the presence of a deformable geofoain panel of low stiffness behind the flexible retaining wall will result in a reduction of the dynamic wall pressures and displacements. The geofoam efficiency in terms of load and displacement reduction decreases as the flexibility ratio of the model wall increases. On the other hand, load reduction efficiency of the geofoam increases as the amplitude and frequency ratio of the excitation increases. Load reduction efficiencies achieved in the tests were compared to those of the previous physical and numerical modeling studies available in the literature. Comparisons indicate that there is an agreement with the data presented in the previous modeling studies for low acceleration amplitudes and wall flexibility values, however, this agreement diminishes as wall flexibility begins to play role in reducing the earth pressures. Application point of the maximum dynamic thrust varies between 0.4 H to 0.6 H depending on the inclusion type, flexibility ratio of the wall and the characteristics of the harmonic motion applied to the base of the models.