Lubricating greases are complex products, consisting of a lubricating fluid, performance enhancing additives and a thickener. The lubricating fluid can be mineral oil, synthetic fluid of various types or even processed vegetable oil. The viscosity of the fluid can range from very low (ISO 10 or less) to very high (ISO 6800 or higher).
Additives are added to grease to provide or enhance various performance properties. The third component of grease, and the one that sets grease apart from fluid lubricants, is the thickener. Multiple types of materials have been used to thicken oil to make grease, with the most common thickeners today being the soaps (salts) of long-chain fatty acids and alkaline earth metals. The reaction of fatty acid with alkali is known as saponification. The thickener is the component of a grease that produces consistency. This, in other words, is the stiffness characteristic of grease.