The expandable polyurethane resin is an innovative material used in the field of soil stabilization and foundation restoration. The injection technology using the expandable polyurethane resin is an effective way that raises the foundations rapidly, strengthening the soil beneath. Nevertheless, different technical aspects have not been studied yet, which might affect the lifting and stabilization process, such as the density of the resin formed in the massive of the injected soils. The density of the resin formed in the massive of the injected soils during the injection process is varied due to the expansion nature of the resin when mixed proportionally controlled by the amount of the injected resin, the injection pressure, the injection temperature, and other factors. Obviously, the differences in resin densities lead to a variation of the resin mechanical properties; consequently, it affects the desired lifting and strengthening results gained. The article demonstrates the results of a laboratory experiment that has been conducted to investigate the mechanical properties of an expandable polyurethane resin consists of two components based on its volumetric expansion ratios controlled by the amount of the injectable resin. The density of the resin gained for each expansion ratio has been obtained and given in this article. The stress-strain diagrams of the resin for various densities and expanding ratios are incorporated. The results were interpreted, and the strength-density relationship of the resin has been established and introduced.