The thermophysical and mechanical properties of a nanocomposite material composed of amine-cured diglycidyl ether of bisphenol A (DGEBA) reinforced with organomontmorillonite clay are reported. The storage modulus at 100 degreesC, which was above the glass-transition temperature (T-g), increased approximately 350% with the addition of 10 wt % (6.0 vol %) of clay. Below the T-g, the storage modulus at 30 degreesC increased 50% relative to the value of unfilled epoxy. It was determined that the T-g linearly increased as a function of clay volume percent. The tensile modulus of epoxy at room temperature increased approximately 50% with the addition of 10 wt % of clay. The reinforcing effect of the organoclay nanoplatelets is discussed with respect to the Tandon-Weng and Halpin-Tsai models. A pseudoinclusion model is proposed to describe the behavior of randomly oriented, uniformly dispersed platelets in nanocomposite materials. (C) 2004 Wiley Periodicals, Inc.