Water-blown flexible polyurethane foams and molded plastic films were made by replacing 0 to 50%, of Voranol (R) 4701 in the B-side of foam and plastic film formulation by epoxidized soybean oil (ESBO). Physical properties of foams including density, 50%, compression force deflection (CFD), 50% constant deflection compression (CDC), and resilience were determined. A dynamic mechanical spectrometer (DMS) and a differential scanning calorimeter (DSC) were used to characterize the hard segment (HS) and soft segment (SS) ratio and thermal properties of plastic. Various functional groups in both flexible polyurethane foam and plastic film were characterized using Fourier transform-infrared spectroscopy with attenuated total reflectance (FTIR-ATR). When increasing the ESBO content, both density and 50% CFD of water-blown polyurethane foams decreased first, then increased. On the other hand, the 50% CDC and resilience of foams showed a sharp increase and decrease, respectively. When increasing the ESBO content, the peak of tan delta in DMS analysis and Delta c(p) in DSC analysis of plastic films both decreased indicating the hard segment increased and the soft segment decreased in plastic film, respectively. The FTIR-ATR results also show the hydrogen-bonded urethane group increased in plastic films with increasing ESBO content. (c) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 111: 1311-1317, 2009