The aim of this investigation is to determine the effect of low-filler volume fraction on the elastic modulus and the thermal expansion coefficient of particulate composites. In the theoretical part, theoretical model valid for low-filler volume fractions is used to evaluate these two magnitudes. In the experimental part, low-percentage filler contents of 3, 5, 7, and 10% are used. The density for these epoxy resin-iron particle composites is also determined. At the same time, an attempt to explain some of the disagreements observed between theoretical values and experimental data on a qualitative basis is also made. This attempt is in part assisted by scanning electron microscopy (SEM) observations concerning structural inhomogeneities and fractographical data. The comparison of the theoretical values derived from the present model with experimental results and with theoretical values derived from other workers appears satisfactory in many cases, but in some others the discrepancies among them are considerable. (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 111: 203-216, 2009