Thermoset-elastomer polyurethane (PU) nanocomposites were prepared using two types of tungsten disulphide (WS2) nanoparticles: inorganic fullerene-like (IF) and inorganic nanotubes (INT) through an in-situ polymerization process. The quality of dispersion was evaluated using scanning electron microscope (SEM) and the thermomechanical properties were analyzed using dynamic mechanical analysis (DMA). Addition of 1% and 3wt.%. IFs resulted in enhancement in storage modulus of 45 and 100%, respectively, compared to the neat polymer. The enhancement using only 0.5% wt. INTs was more than 100% and then decreased with additional amount of nanotubes. While no significant change in the composite's glass transition temperature (T-g) was observed with IF-WS2, 0.5% INT-WS2 showed a 20 degrees C increase of T-g. In both cases, analysis of the chemical structure using an attenuated total reflectance- Fourier transform infrared spectroscopy showed no effect of the nanoparticles on the chemical structure of the PU and wide-angle X-ray diffraction showed no change in morphology. In the case of IF-WS2 the highest peel strength was obtained with 1% wt. demonstrating a 44% improvement in peel strength. However, in the case of INT-WS2, incorporating 0.5% wt. improved the peel strength by more than 1000%. SEM analysis showed a unique development of a nodular morphology and a failure mechanism dominated by nanotube pull-out. It was concluded that the geometry of the nanoparticles (nanotubes or fullerene) has a dominant effect on the final PU nanocomposite properties.