The focus of this work was to synthesize bio-based polyurethane (PU) foams from soybean oil (SO). Different polyols from SO were produced as follows: soybean oil monoglyceride (SOMG), hydroxylated soybean oil (HSO), and soybean oil methanol polyol (SOMP). The SOMG was a mixture of 90.1% of monoglyceride, 1.3% of diglyceride, and 8.6% of glycerol. The effect of various variables (polyol reactivity, water content curing temperature, type of catalyst, isocyanate, and surfactant) on the foam structure and properties were analyzed. SOMG had the highest reactivity because it was the only polyol-containing primary hydroxyl (-OH) groups in addition to a secondary -OH group. PU foams made with SOMG and synthetic polyol contained small uniform cells, whereas the other SO polyols produced foams with a mixture of larger and less uniform cells. The type of isocyanate also had an influence on the morphology, especially on the type of cells produced. The foam structure was found to be affected by the water and catalyst content, which controlled the foam density and the cure rate of the PU polymer. We observed that the glass transition (T-g) increased with the OH value and the type of diisocyanate. Also, we found that the degree of solvent swelling (IDS) decreased as T-g increased with crosslink density. These results are consistent with the Twinkling Fractal Theory of T-g. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 2567-2578, 2009