The invention relates to a coating composition for making a porous inorganic oxide coating layer on a substrate, the composition comprising an inorganic oxide precursor as binder, a solvent, and a synthetic polyampholyte as pore forming agent. The size of the pores in the coating can be advantageously controlled by the comonomer composition of the polyampholyte, and/or by selecting conditions like temperature, pH, salt concentration, and solvent composition when making the composition. The invention also relates to a method of making such coating composition, to a process of applying a coating on a substrate using such composition, and to such coated substrate showing a specific combination of optical and mechanical properties.