Recent developments concerning the methodology used to prepare composites of iPP and nanoclays are reported. Conventional (reactive melt mixing) and in situ preparations were performed, and the structural properties exhibited by the composites are discussed. Results suggest that the nanoclay could exhibit partial and, maybe, total exfoliation within the composites. Adhesion between the polymeric matrix and the nanoclay layers is similar to that obtained after grafting. The experimental procedure used and the analysis performed by means of the wide-angle X-ray scattering and differential scanning calorimetry techniques permit to describe, at nanoscale level, the contribution of the nanoclay to the polymer composite system. The microhardness values of the iPP-clay composites depend on the clay content and on the preparation method, and linearly correlate, according to the additivity law, with the degree of crystallinity. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 115: 2654-2662, 2010