Self-cleaning coatings are one of the technologies that have various applications today due to the reduction of maintenance costs. The purpose of this study is to create a water-repellent polymer-based nanocomposite coating on an aluminum sheet and glass and to investigate the free energy of its surface. Initially, silica nanoparticles modified with hexamethyldisilazane were used as the reinforcing phase and ethylene-vinyl acetate as the matrix and toluene as the solvent. After combining polymer and solvent with the concentrations of 1%, 3%, and 5%,the 3% concentration was selected as the optimal concentration for film formation on the surface. To achieve high static contact angle and low sliding angle, the percentages of 1%, 10%, 20%, and 30% by weight of polymer nanomaterials were added to the solution. The spraying method was used to cover the surface due to its one-step as well as its cost-effectiveness and the possibility of large-scale use. The scanning electron microscopy images of samples with a high weight fraction of nanomaterials had a porous and lattice structure that indicated a cassie-baxter state. Its degree and sliding angle reached 8 degrees. The surface roughness results confirmed the increase in surface roughness with an increasing content of nanomaterials in the coating. Three theories of Owens-Wendt, Fowkes and Van Oss were used to study the surface free energy. Fowkes and Owens-Wendt theories showed that with increasing the concentration of nanomaterials, the polar component of the free energy of the coating surface decreased, but Van Os's theory did not correctly predict the polarity of the surface. Keywords: Polymer-based nanocomposite, hydrophobic coating, surface free energy, contact angl, Roughness