Structural characterization in polymer nanocomposites is usually performed using X-ray scattering and microscopic techniques, whereas the improvements in processing and mechanical properties are commonly investigated by rotational rheometry and tensile testing. However, all of these techniques are time consuming and require quite expensive scientific equipment. It has been shown that a fast and efficient way of estimating the level of reinforcement in polymer nanocomposites can be performed by melt extensional rheology, because it is possible to correlate the level of melt strength with mechanical properties, which reflect both the 3D network formed by the clay platelets/polymer chains as well as final molecular structure in the filled system. The physical network made of silicate filler and polymer matrix has been evaluated by X-ray diffraction and transmission electron microscopy. Extensional rheometry and tensile testing have been used to measure efficiency of the compatibilizer amount in a polypropylene-nanoclay system. (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 111: 2253-2259, 2009