The study investigated an approach to incorporate modified epoxidized soy-based vegetable oil polyol as a replacement for petroleum-based polyether polyol and to substantially reduce the isocyanate loading in the rigid foam formulation. Noncatalytic polymerization of epoxidized bodied soybean oil and ethylene glycol (EG) was carried out in a closed batch reaction. Cleavage of the oxirane rings and hydroxyl group attachment at optimum conditions provided the desired polyol products. The polyols were characterized based on its hydroxyl numbers, acidity, viscosity, iodine number, and Gardner color index for quality purposes. Reactions of oxirane ring and EG were verified by spectroscopic FTIR. Crosslinking performance was evaluated by extractability analysis on the poly-Urethane (PU) elastomer wafers. Rigid foaming performed at 50 and 75% petroleum-based polyether polyol replacements have shown excellent thermoinsulating and mechanical properties compared with epoxidized soybean oil (ESBO) alone or petroleum-based polyether polyol alone. A reduction of up to 8% of the polymeric diphenylmethane diisocyanate was achieved using the synthesized ESBO-EG-based polyols. A higher average functionality polyol is key component to the reduction of isocyanate in PU synthesis. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 2185-2194, 2009