<p>This research investigates the mechanical properties of thermoplastic polyurethane (PU) reinforced with nanodiamonds (ND) at 0.1, 0.2, 0.3, and 0.5 weight % using experimental and FEM simulation approaches using Ansys software. Representative volume elements (RVEs) were carefully designed of size 1×1×1 µm with spherical-sized randomly distributed ND particles to mimic a similar weight percentage as the experimental approach. It is observed that Young’s modulus obtained from the experimental approach at different weight fractions is closer to RVE prediction and other micromechanical models, such as the Halpin-Tsai, Clyne-Davis, and Eshelby models. Mechanical testing revealed a substantial improvement in tensile strength and modulus with increasing ND content, with the 0.5 wt.% ND sample exhibiting the most significant enhancement. Flexural properties were similarly improved, indicating greater stiffness and resistance to deformation. SEM fractography provided additional insights, showing a ductile fracture surface in the pure PU matrix, while the 0.5 wt.% ND-reinforced sample displayed a more brittle fracture behavior, indicative of the stiffening effect of the fillers. FEM simulation is performed, and it is observed that the deviation from the experimental approach lies within a 10 % error margin. These findings highlight the potential of ND filters in tailoring the mechanical properties of PU-based polymer nanocomposites, with implications for advanced engineering applications.</p>