In the current work, the influence of filler particle size on the performance of the composites was studied. Some physical parameters were measured for linear low-density polyethylene (LLDPE) films reinforced with silicon dioxide (SiO₂) powder. Samples filled with SiO₂ of different particle sizes and concentrations were prepared. It was found that fillers with small size caused an increase in mechanical properties of LLDPE at lower concentration than that of particles with bigger size. This was confirmed experimentally by measuring different physical parameters such as yield strength, coefficient of thermal expansion, thermal conductivity, melting temperature, and structural morphology. Therefore, filler sizes ranged from nano to micro could help in reducing the amount of the usage of filler, which could overcome the recycling problems of the filled polymers without affecting the end-use properties of the composite. Illustrations are given using figures, images, and tables.