Both rigid and flexible water-blown polyurethane foams were made by replacing 0-50% of Voranol (R) 490 for rigid foams and Voranolc (R) 4701 for flexible foams in the B-side of foam formulation by epoxidized soybean oil. For rigid water-blown polyurethane foams, density, compressive strength, and thermal conductivity were measured. Although there were no significant changes in density, compressive strength decreased and thermal conductivity decreased first and then increased with increasing epoxidized soybean oil. For flexible water-blown polyurethane foams, density, 50% compression force deflection, 50% constant force deflection, and resilience of foams were measured. Density decreased first and then increased, no changes in 50% compression force deflection first and then increased, increasing 50% constant force deflection, and decreasing resilience with increase in epoxidized soybean oil. It appears that up to 20%) of Voranol (R) 490 could be replaced by epoxdized soybean oil in rigid polyurethane foams. When replacing up to 20%) of Voranolc (R) 4701 by epoxidized soybean oil in flexible polyurethane foams, density and 50% compression deflection properties were similar or better than control, but resilience and 50% constant deflection compression properties were inferior. (c) 2008 Wiley Periodicals, Inc.