The aim of this study is to clarify the dynamic properties of rigid polyurethane foam. A method for renovating a deteriorated bridge as a lightweight embankment was proposed. The space underneath a bridge is filled with polyurethane to support the upper structure. In this case, the upper structure of the bridge is considerably heavier than the polyurethane. Therefore, it is important to examine the seismic behavior of this new lightweight embankment. However, the dynamic deformation characteristics of polyurethane have not been clarified previously. In this study, stress-controlled cyclic triaxial tests based on JGS0542-2009 are used to evaluate the effect of the confining stress and the presence of a rigid layer on the dynamic properties of rigid polyurethane foam. As a result, the shear modulus of rigid polyurethane foam increases with increasing confining stress regardless of the absence of the rigid layer. The shear modulus of polyurethane with the rigid layer is lower than that of polyurethane without the rigid layer. The value of shear modulus of rigid polyurethane foam was measured in the range of approximately 1.6~3.2MPa. Moreover, the stiffness degradation and of rigid polyurethane foam are in good agreement with the Hardin-Drnevich model.