Flowable restorative composites that are unique for clinical application performances, both in mechanical and physico-chemical properties as well as flowability, were developed through the modification of A200 and M8000 silica particle surfaces with various silane-based coupling agents. The presence of the coupling agent used in particle surface modification for matrix-particle interface formation was specified with thermogravimetric analysis and Brunauer–Emmett–Teller surface area analysis while the bonding was specified with Fourier Transform Infrared and X-Ray Photoelectron spectroscopy analysis. Flexural strength, compressive strength and water sorption, which are considered to be important tests in this field, were conducted and studied. Flowability was examined keeping clinical application performances in mind. The increase in silanization activity that is dependent on the length and volume of the active unit belonging to the coupling agent decided by the dispersion of modified silica particles in the matrix is linearly related to the active unit quantity of the coupling agent. Active unit quantity, which is also linearly related to the flowability of the composite, affects mechanical and physico-chemical properties of the composites. The flow distances and rates of the produced composites are in the range of 0.63–3.43 cm and 0.11–0.57 mm/s, respectively. different composites in the flowable composites class, which are generally adopted in the area of dental composites, have been produced. The created interface changed the rheologies of the composites, resulting in a change in flow distances and rates, and composites exhibiting similar flow behavior as commercial flowable composites were obtained.