A series of nanocomposites was prepared with two different methods leading to different levels of exfoliation, and the dynamic properties were measured in the solid state and the melt. The results were compared with micro-composites containing various shapes of glass filler. The higher modulus of nanocomposites at higher concentrations is accompanied by an increase in melt viscosity and the occurrence of a yield stress in the melt. The modulus at room temperature and the melt viscosity are influenced by the aspect ratio and the concentration of the filler particles. These results were used to calculate the aspect ratios of the reinforcement using the Halpin-Tsai composite model and several modified Einstein viscosity models. The experiments showed that the Simha theory for oblate and prolate spheroids predicts platelet aspect ratios from melt viscosity data that are close to the results from the Halpin-Tsai composite model and from TEM observations. The results of the analysis show the advantages and disadvantages of the various shapes and sizes of fillers and the level of exfoliation, both from a processing and a mechanical properties point of view. (c) 2005 Elsevier Ltd. All rights reserved.