Significance Currently, the effect of branching of nanoparticles tens of nanometers in size on the mechanical properties of structural composites is not well understood due to the limited availability of branched nanoscale fillers. We report that branched nanofillers have the potential for optimization of nanocomposite Young’s modulus over their linear counterparts. Lattice spring model simulations reveal that the mechanism for this improvement involves the ability of branched nanoparticles to optimize the ratio of both filler and stiff interfacial bonds aligned with the tensile axis, as opposed to linear nanoparticles, which optimize only the filler bond orientation when parallel to the stretching axis. We believe this information could inform the design of nanocomposites with optimized mechanical properties for a variety of structural applications. With the availability of nanoparticles with controlled size and shape, there has been renewed interest in the mechanical properties of polymer/nanoparticle blends. Despite the large number of theoretical studies, the effect of branching for nanofillers tens of nanometers in size on the elastic stiffness of these composite materials has received limited attention. Here, we examine the Young's modulus of nanocomposites based on a common block copolymer (BCP) blended with linear nanorods and nanoscale tetrapod Quantum Dots (tQDs), in electrospun fibers and thin films. We use a phenomenological lattice spring model (LSM) as a guide in understanding the changes in the Young's modulus of such composites as a function of filler shape. Reasonable agreement is achieved between the LSM and the experimental results for both nanoparticle shapes—with only a few key physical assumptions in both films and fibers—providing insight into the design of new nanocomposites and assisting in the development of a qualitative mechanistic understanding of their properties. The tQDs impart the greatest improvements, enhancing the Young's modulus by a factor of 2.5 at 20 wt.%. This is 1.5 times higher than identical composites containing nanorods. An unexpected finding from the simulations is that both the orientation of the nanoscale filler and the orientation of X-type covalent bonds at the nanoparticle-ligand interface are important for optimizing the mechanical properties of the nanocomposites. The tQD provides an orientational optimization of the interfacial and filler bonds arising from its three-dimensional branched shape unseen before in nanocomposites with inorganic nanofillers.