What is the heat transfer method in soap making?

Have you ever heard of heat transfer? More and more soap makers are switching to this method of soap making. But what does heat transfer actually mean? And should you like many others switch to this advanced method of soap making? Let’s find out!

What is the heat transfer method in soap making? The heat transfer method is a variation of the cold process method in which you use hot lye to melt the hard oils used in the formulation. You don’t need to use external heat, and therefore it also saves more time. This method, however, is trickier than the conventional way of making soap.

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Handmade soap is not always a simple process, and it’s even more complicated when you’re using the heat transfer method. But if I can do it, so can you! We will go through in detail what this technique is all about and how to master it.

What is the heat transfer method in soap making?

When making soap using the cold process method, you’d gradually heat the oils and lye gradually until they’re at 130 degrees Fahrenheit or so before mixing them together and continuing with your soap-making procedure.

The heat transfer method is slightly different. In this method, you keep your liquid oils separate from the hard oils. Then heat the lye until it’s dissolved. At this stage, the lye gets super hot. Now you have to pour the lye over hard oils and let them melt together. Once you start pouring, you’ll see that they start melting as soon as you pour the hot lye.

Now you’d need to stir constantly till all the solid pieces are melted. In most cases, this should not take you more than 10 minutes. At this stage, you can use a stick blender to give a uniform texture to this paste if you have one. If not, just keep on stirring with whatever item you wish to use. Once all has been mixed, and the paste has a nice texture, you can add the liquid oils, mix them again with the blender, or stir. 

Then you can start adding the soap dyes and fragrance oils. Once all are mixed, gradually pour this mixture into your desired mold.

When making room temperature cold process, exothermic heat is produced by the reaction of acids and bases present in the fatty acids and the lye solution. 

In traditional methods of producing cold-process soaps, one would have to melt solid fats like tallow or coconut oil until they were turned completely fluid at room temperature; this becomes an emulsion that’s properly combined with raw materials such as water and potassium hydroxide (lye).

Is the heat transfer method the same as Room Temp Cold Process?

You can also make perfectly beautiful soaps without using an external heat source to melt the solid oils. These “soap” recipes are often called cold process, which you might have heard referred to as room temperature soap making. The terms heat transfer method and room temperature cold process are often used interchangeably for the same method.

The heat transfer method is actually a variation of the cold process soap-making method. We already discussed the difference between the conventional cold process method and the heat transfer method, especially regarding how to melt and mix your ingredients.

But heat transfer is basically a much more convenient way of making soap because it does not require you to wait until the hard oils and lye get cool before mixing both. Neither do you need to use ice baths and cold water to lower the temperature? You don’t need to use any thermometer for making a room temperature cold process soap. 

In this process, no additional heat is required to accelerate the saponification process. In total, the saponification process requires 18 to 24 hours for completion. 

Should you use the heat transfer method?

The process of soap making is a personal choice that should be considered carefully. The most popular methods are the cold and hot processes. However, there’s an additional heat transfer method as well, which some may find more convenient or time-saving.

All three methods – hot, cold, and heat transfer- are similar in using the recipes and combining ingredients. However, the difference is that whether you use an external heat source to start the gel phase of the self-generated heat of soap is used to initiate the gel phase.

Using the heat transfer method is a little bit more tricky;

If you are using a greater amount of solid oils, you need to make sure that every bit of hard oil is melted. Otherwise, you may end up with soap with fat clumps in it. 

Most people don’t rely on this method, and they don’t feel satisfied unless they melt the hard oils by themselves to produce a uniform fat composition.

How to properly do a heat transfer method?

But let’s say you want to give it a try. But are not entirely sure how to start and do this correctly. No worries, here is an easy way to do the heat transfer method.

  • Weigh all your ingredients carefully.
  • Place the hard oils such as butter, coconut, palm oil, lard, or whatever you are using in a container.
  • Weigh the liquid oils and keep them in a separate container.
  • Prepare the lye solution: carefully weigh the water and sodium hydroxide. Add sodium hydroxide to water slowly and gradually while stirring in between to dissolve the crystals.
  • At this stage, the lye solution is very hot, and we are going to use this heat to melt the solid oils.
  • Slowly and carefully add the lye solution to the bowl containing hard oils.
  • Stir the mixture to dissolve oils. It will take a little bit of your time and patience to melt the fat completely.
  • Once the fat is melted, it’s time to add the liquid oils.
  • Stir constantly; you can use a stick blender to make a uniform mixture.
  • Alternatively, blend with short bursts of a stick blender and hand stirring until the soap is in the form of a thin paste.
  • At this stage, you can add soap dyes, fragrance oils, and other additives to it.
  • Then pour the soap mixture into molds. 
  • When the soap gets cold, remove it from molds, cut it into bars, and set it away to cure.
  • The soap will approximately require a cure time of 4 to 6 weeks.


Heat transfer is a tricky and difficult technique. It may not seem as popular, but it’s important to try it out if you want something different from the more common hot or cold process soap-making methods. But if you think about it for a second, how many people are talking about the heat transfer method? Not as many as cold or hot process, right? Well, this clearly shows in my opinion that this technique is not used a lot, probably due to its difficulty.

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