The influence of octakis(n‐hexadecyldimethylsiloxy)octasilsesquioxane (hdPOSS) on rheological and thermal properties of linear low‐density polyethylene was investigated. Rheological evaluations realized by two different measuring techniques (rotational and extensional rheometry) allowed to obtain a wide range of information concerning an influence of silsesquioxanes on rheological properties of polymeric matrix. The studies were complemented with Differential Scanning Calorimetry measurements. In order to evaluate the miscibility of thermoplastic matrix and hybrid organic‐inorganic nanosized filler, rheological investigations, Dynamic Mechanical Thermal Analysis and Scanning Electron Microscopy were applied. Simultaneously, based on the rheological and thermal investigations, the mechanism of interactions between polymeric matrix and silsesquioxanes was considered. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42825.