The role of thinners in paints: Solubility: For different systems of paint, different types of solvents need to be used. Because not all solvents can dissolve the same resin. The dissolution of the solvent to the resin follows the principle of similar polarity, the principle of similar solubility parameters and the principle of solvation. A good diluent formulation will contain true solvent, co-solvent and diluent, and achieve some balance.