What is Cold Process Soap?

Mary McMahon
Mary McMahon

Cold process soap is a soap which is known for being hard and durable. This soap can be manipulated in a number of different ways to add moisturizing properties, scents, and so forth. Many bar soaps available in the store are cold process soaps, as are many hand soaps. It is also possible to make cold process soap at home, with the proper equipment and training.

Crushed walnut shells can be added to cold process soap as an exfoliant.
Crushed walnut shells can be added to cold process soap as an exfoliant.

When soap is made, a chemical reaction known as saponification occurs. This reaction happens as lye and fats are mixed and then allowed to sit. If the proportions are right, the chemical structure of the mixture changes, creating the material people recognize as soap. If the proportions are wrong, the “soap” may stay mushy, may be caustic in nature, can feel greasy, or may turn gelatinous in a way which was not intended.

Essential oils are often included in cold process soaps.
Essential oils are often included in cold process soaps.

The term “cold” in “cold process soap” is actually a bit of a misnomer, because things get quite warm. Soapmakers start by making a lye mixture and allowing the mixture to cool, and then liquefying fats and oils and bringing them to a temperature close to that of the lye. Cold process soap is made at a temperature a bit higher than body temperature, as a general rule. Then, the lye and fats are blended. As they blend, they will warm up because of the chemical reaction occurring. When the mixture turns thick, reaching a state known as “trace,” additives such as essential oils, colors, and inclusions like flower petals can be blended in.

Cold process soap is made by mixing a water and lye solution with oils such as olive, coconut, and palm.
Cold process soap is made by mixing a water and lye solution with oils such as olive, coconut, and palm.

The soap mixture is poured into molds and kept in an insulated place to allow the chemical reaction to continue taking place. After around 24 hours, the cold process soap can be unmolded and cut, if necessary. Next, it needs to cure; cold process soap can take up to six weeks to fully cure. The properties of the soap can be varied by using different fats in different proportions, and by using inclusions; for example, a gentle exfoliating facial soap can be made with ground walnut shell or coffee mixed into the soap.

It is necessary to use a saponification chart when making cold process soap. This chart provides information about the correct proportions of lye to fats needed for various fats to saponify properly. People also need very precise scales and protective equipment such as gloves, because working with lye can be extremely dangerous. It is also advisable to make cold process soap outside, to avoid inhaling the gases associated with the saponification reaction.

Many bar soaps are cold-process soaps.
Many bar soaps are cold-process soaps.
Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a wiseGEEK researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

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Discussion Comments


I have to buy distilled water when making cold process soap. I live in an area that has hard water, and this can affect the reaction negatively.

When I was learning how to make soap this way, I was shocked to learn that once you add the water to the lye and mix it, it can reach up to 200 degrees! Also, the amount of water you add is crucial.

I once added too much water, and my soap turned out mushy. The next time, I overcompensated and put too little water in, and the soap was harsh and dry.

It was a long process, but I think I've finally got the proper method down. It's nice to finally know how to make cold process soap without relying on someone else's expertise and instructions.


I tried making cold process soap once, but I failed miserably. It just turned to mush and stayed that way.

I am jealous of my crafty friends who seem to have a knack for making soap in this way. I think that soapmaking is like cooking. Some people are naturally good at it, while others can't seem to get the hang of it, even though they try time and time again.

I wanted to make cold process soap, so that I could put bits of almond shell in it. Years ago, my favorite exfoliating soap contained almond shell, but they don't make it anymore. I had hoped to replicate it, but it looks as if I will have to call on my skilled friends for help.


@cloudel – I love coffee soap. The rough grounds make it a good exfoliator, and the scent is amazing.

In addition to smelling good, it also has the power to take the odor of fish, onion, and garlic out of my hands. I frequently cook these things, and regular soap just doesn't take away the aroma.

When I use it on my face, it really wakes me up. I think that the caffeine in it stimulates my skin, making me look more awake. Then, of course, there is the smell, which I associate with drinking coffee and perking up.

I would definitely recommend trying it. If her soap is anywhere near as good as the one I use, then you will probably fall in love with it.


My friend has a shed out back with one wall open to the elements, and this is where she concocts her cold process soap recipes. She doesn't want to endanger her children with the fumes and ingredients, so she always does her soapmaking out there.

She adds orange essential oil to one soap that I have come to love. It is extremely citrus-scented, and the smell fills up my entire bathroom as I use it.

She has been trying to get me to test out her new coffee scrub soap. It just seems strange to me. Has anyone here ever used coffee soap?

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