What Is Cold Process Soap? How It Is Made and Why It Cures
By Kanna Botana ·
Cold process soap is soap made from scratch by mixing oils and butters with lye at low temperature, pouring the mixture into a mold, then letting the bars cure for several weeks. It is the traditional way handmade bar soap is made, and it gives the soapmaker full control over every oil, butter and scent in the bar.
How cold process soap is made
Every true soap starts with a chemical reaction called saponification. Fats and oils react with an alkali, sodium hydroxide (lye) for bar soap, and turn into two things: soap and glycerin.
- Weigh the oils and butters. Each one changes the finished bar. Olive oil adds mildness, coconut oil adds big bubbles and cleansing power, castor oil boosts lather, and shea butter or tallow add hardness and creaminess.
- Mix the lye solution. Lye is dissolved in water and allowed to cool.
- Combine at low temperature. The lye solution goes into the oils and is mixed until it thickens to "trace," the texture of thin pudding.
- Add scent, color and botanicals. Essential oils, fragrance, clays and dried flowers go in at this stage.
- Pour, set and cut. The soap sits in the mold for a day or two, then gets cut into bars.
- Cure. The bars rest on racks for weeks before they are ready to use.
In a properly formulated bar, the lye is used up during saponification. What is left is soap, glycerin, and a small amount of extra oil that soapmakers leave in on purpose so the bar feels gentle.
Why cold process soap cures for four to six weeks
A freshly cut bar is still soft and full of water. During the cure, that water evaporates and the bar finishes setting. The result is a harder bar that lasts longer in the shower and feels milder on skin. That is why every bar in our Cleanse collection cures for four to six weeks before it ships. It is the slow part of the process, and the part that makes the biggest difference.
The glycerin stays in the bar
Glycerin is a humectant, which means it draws water toward your skin. Saponification creates glycerin naturally, and in cold process soap it simply stays in the bar. That is a big part of why a well-made handmade bar can leave skin feeling comfortable instead of tight.
Cold process vs melt and pour vs hot process
| Cold process | Melt and pour | Hot process | |
|---|---|---|---|
| Made from | Raw oils, butters and lye | A premade soap base, melted down | Raw oils, butters and lye |
| Heat | Low | Melted to pour | Cooked to speed up saponification |
| Control over ingredients | Full | Limited to what is in the base | Full |
| Texture | Smooth, can hold swirls and toppings | Smooth, often clear or glossy | Rustic and textured |
| Cure time | About 4 to 6 weeks | Ready once it sets | Usable sooner; still improves with a cure |
None of these methods is wrong. Cold process is simply the one that lets a maker build a bar from the oils up, which is why we use it.
What the oils do in a bar
- Olive oil: a mild, conditioning base.
- Coconut oil: fluffy lather and cleansing power.
- Castor oil: boosts and stabilizes the lather.
- Shea butter: a creamier, harder bar.
- Hemp seed oil: a light oil rich in essential fatty acids. See our guide to hemp seed oil for skin.
- Beef tallow: a traditional fat that makes a hard, long-lasting bar with dense lather. Read tallow soap benefits.
- Clays: kaolin and rose clay add slip and a silky feel.
Every product page lists the full ingredients, so you can see exactly what is in each bar before you buy.
How to use and store a handmade bar
- Let it drain. A bar sitting in water turns soft and wears away fast. A slatted wooden soap holder or an exfoliating soap saver keeps it dry between uses.
- Keep it out of the shower stream. A shelf away from direct spray can add weeks to a bar's life.
- Store spare bars cool and dry. A drawer or linen closet works well and keeps the scent fresh.
- Cut big bars in half. Use one half while the other stays dry.
Shop cold process soap
Every bar in our Cleanse collection is hand-poured in small batches in Temecula, California and cured four to six weeks. Try Hemp + Wildflower for a floral, kaolin clay bar with hemp seed and baobab oils, or browse the tallow soap bars for a denser lather.
Cold process soap FAQ
Is there lye in cold process soap?
Lye is needed to make soap, but in a properly formulated and cured bar it reacts with the oils and is used up. The finished bar is soap and glycerin, not lye.
Is cold process soap good for dry skin?
Many people with dry skin prefer handmade bars because the glycerin stays in the soap and makers leave in a little extra oil. Everyone's skin is different, so patch test a new bar if your skin is sensitive.
How long does a bar of cold process soap last?
It depends on how often you use it and how dry it stays. A well-cured bar that drains between uses lasts much longer than one left in a wet dish.
Why does handmade soap cost more than store-bought soap?
Small batches, whole oils and butters, and weeks of curing time all add cost. You are paying for a bar built from scratch rather than a mass-produced one.