The modulus and coefficient of thermal expansion (CTE) of polypropylene-based nanocomposites and blends were predicted using various composite theories and compared to experimental results. The Mori-Tanaka and Chow model predictions best match the previously reported experimental trends, though the Chow model underestimates the CTE in the normal direction (ND). Of the various ternary-phase approaches used to predict the modulus and CTE of thermoplastic polyolefin (TPO) nanocomposites, a multiplicative approach wherein the contribution of the clay is calculated first and the nanocomposite is then considered to be the matrix for the elastomer blend best matches the experimental trends. The models better capture the effects of the MMT than those of the ethylene-octene elastomer, EOR. A different model predicting the effect of the MMT tactoids on the experimental TPO gives rather good quantitative agreement between the predicted and experimental values of modulus and CTE for TPO nanocomposites. (C) 2011 Elsevier Ltd. All rights reserved.