What is Cold Process Soap Making?

Cold process method is a way to make soap without applying any extra heat. By definition, it is impossible to make really "cold" soap. This is because soap is the product of a chemical reaction (called "saponification") where fatty acids, combined with an alkali, give a salt as the final product.
For saponification to occur, oils, fats and the alkali must all be in liquid form. For this reason, water is needed to dilute the alkali, and oils or fats that are solid at room temperature must first be placed on a heat source to melt.

The alkalis used for soap making are sodium hydroxide and potassium hydroxide. In their pure form, both sodium hydroxide and potassium hydroxide are solid (powder or flakes). When we talk of "alkali", we refer to sodium or potassium hydroxide, in general. When we talk of "caustic soda", we usually refer to the same thing - whereas a "caustic solution" or "lye solution" is the strongly alkaline liquid made by dissolving pure sodium hydroxide and potassium hydroxide in water.

In case you're wondering, there is no way of making soap, and even less natural glycerin soap, without an alkali. For the fatty acids (fats and oils) to turn into soap, caustic soda must be used - no alkali, no chemical reaction, no salt and no soap. However, properly made natural soap contains some extra fatty acids (which are very good for your skin), plenty of natural glycerin (which is good for your skin), and no free alkali - which is quite the opposite of what happens with factory soaps... even the mildest!