There are several different ways to creating a bar of soap. This is a brief overview of the most popular methods you will read about.
Melt & Pour method
This method is where the soap has already been made in a factory. It is presented as a solid block of soap which is cut into smaller chunks, melted over heat (usually in a microwave) into a liquid, poured into a mould and left to set. Additonal items such as fragrance and colour can be added easily when the soap is in this liquid state.
It is popular because it is easy to make good looking bars of soap, is safe to use and is very quick. A bar of soap can be made in a couple of hours.
Cold Process method
This is where soap is created from scratch using all the ingredients . It is where the chemical reaction between an oil and lye form soap. It is called cold process because no heat is added to the process other than the heat required at the beginning to melt the oils. The base oils typically used include olive oil, coconut oil and palm oil. The soap maker has complete control over the ingredients and many different variations of soap can be made. However, it does involve the use of chemicals (sodium hydroxide aka lye) and it does require the soap to be left to cure for 4-6 weeks after it is made.
Hot Process method
The hot process method involves adding heat in order to quicken the saponification process. It is similar to the cold process method in using ingredients to make the soap from scratch but after the trace stage the soap is cooked in a slow cooker or double boiler. The advantages are that the soap is fully saponified quickly and can be used after a few days rather than weeks.