The flexural modulus of oak and pine boards suffused with polymeric methylene diphenyl diisocyanate (pMDI) was measured as a function of the amount of pMDI imbibed. The resulting modulus values were compared to predicted values calculated by assuming a relationship between the composite phases. Specifically, the measured flexural moduli were compared to values obtained from a Kerner model, in which the composite phase consists of isolated and spherical particulate isotropically arranged in the major phase. Results were also compared to a Davies model, in which the two phases exist in a bonded co-continuous morphology. The measured data was shown to be well fit to the Kerner model and not well described by the Davies model, despite the fact that the Davies model is more physically descriptive of the filled wood pore structure. This incongruous result indicates that the pMDI/wood interface is weak, and the resulting tensile properties are not significantly different from the wood-air composite in the absence of pMDT. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 113: 1739-1744, 2009