In fact, most fatty acids are longer than octanoic acid. Solid lipids are generally called fats . Saturated fats contain saturated fatty acids and are solids at room temperature. Lard, and butter are examples of saturated fats. Soap made from these fats tends also to be solid at room temperature.
Unsaturated fats contain unsaturated fatty acids and are liquids at room temperature.
Generally called oils , examples include corn oil and safflower oil. These oils produce liquid soap. While unsaturated fats are generally more healthy than saturated fats, many times a liquid fat is not convenient. To make soap, we must break the fat into its fatty acid and glycerol constituents. The fatty acid has a long hydrocarbon tail which is soluble in fats, and a polar oxygen end which is soluble in water.