When traditional soaps are made glycerin (a vegetable based humectant) in that mixture rises to the top. Manufacturers remove that glycerin and use it to make lotions and creams. Soaps made without a humectant will leave your skin clean, but dry and may be called beauty bars instead of soap.
The Food and Drug Administration says that a soap must be made with 4 basic ingredients: Liquid(s): water, juice, milk or aloe, etc; Oils: olive, grapeseed, sunflower, etc; and/or Butters: cocoa, shea, or mango, etc, and Lye. When a specifically measured mixture containing ingredients from these 4 categories are combined, they may be heated or allowed to heat on their own but the process of heating that mixture may reach 200 degrees or more, but once that mixture has cooled to 99 degrees or less, it has saponified and become soap.
Or, "soaps" that are not all natural are called
Hand made soaps retain all the oils and butters used and good soap use what is called "superfat" which is usually some type of a butter (cooa, mango or shea, etc).
humectants include glycerin, seaweed, aloe vera gel, hyaluronic acid, and honey.