A symmetric and interconnected skeleton structural (SISS) model is proposed for predicting the thermal and electrical conductivities and Young’s modulus of open-cell foams with hollow and solid struts. The model predicted the effective thermal and electrical conductivities of solid-strut aluminium foams and other open-cell foams for the entire porosity range. The SISS model provided upper and lower bounds for the effective thermal conductivity and Young’s modulus of hollow-strut open-cell nickel foams. The SISS model was also found to predict the effective thermal conductivity of closed-cell graphite foams, and the effective electrical conductivity and Young’s modulus of closed-cell aluminium foams with reasonable accuracy. By analogy, the SISS model might also be applied to other physical properties.