The kinetics aspects of the formation of castor-oil-based polyurethane/poly(2-hydroxyethyl methacrylate) interpenetrating polymer networks (IPNs) were studied. The effect of parameters such as the polyurethane content, the activator, and acrylic cross-linker on the kinetics of formation of IPN networks was examined at room temperature. The formation of the individual networks, polyurethane, poly(2-hydroxethyl methacrylate), and their IPNs, was studied by measuring the decrease of absorbance of characteristic absorption peak of each system using IR spectroscopy.