What Is Cold Process Soap? The Old-School Way Real Soap Is Made
If you’ve spent any time shopping for handcrafted soap, you’ve probably seen the words cold process soap thrown around.
Sounds important. Maybe a little mysterious.
But what exactly does “cold process” mean?
At its core, cold process is one of the oldest and most traditional ways of making real soap. Instead of starting with a premade soap base, cold process soap is made from scratch by combining oils and fats with lye and allowing a chemical reaction called saponification to transform those ingredients into soap.
That’s how every bricc at Brick Box begins.
No premade base. No melting down somebody else’s soap.
We start with oils, fats, lye, and a recipe—and build the soap from the ground up.
So, What Is Cold Process Soap?
Cold process soap is made by combining fats and oils with an alkaline solution, usually sodium hydroxide—better known as lye.
When they’re mixed in the correct proportions, something pretty remarkable happens.
The oils and lye react with one another through a process called saponification. The original ingredients are chemically transformed into something new: soap and naturally occurring glycerin.
In other words, we aren't simply mixing ingredients together and waiting for them to harden.
We’re actually making soap.
And once saponification is complete, the lye used to create the soap has been consumed by that reaction. A properly formulated and properly made finished bar does not have free lye sitting around waiting to attack your skin.
Which brings us to one of the biggest questions people have about handmade soap.
Wait—There’s Lye in Soap?
Yep.
And that's a good thing.
Lye sometimes gets treated like the villain of soapmaking because sodium hydroxide by itself is extremely caustic. Soapmakers absolutely have to handle it carefully.
But without an alkali like lye, you don't get real soap.
You get oils.
Once the lye reacts with the oils during saponification, those raw ingredients are transformed. Think of it a little like baking a cake: the eggs, flour, butter, and sugar you started with aren't sitting unchanged inside the finished cake.
Chemistry happened.
Soapmaking works the same way.
So when you see sodium hydroxide involved in cold process soap, don't panic. It's not some strange additive somebody dumped into the bar.
It's part of the process that makes soap possible in the first place.
Why Is It Called “Cold” Process?
The name can be a little misleading.
Cold process soapmaking isn't necessarily cold.
The oils may need to be warmed. Some solid fats and butters have to be melted. And the reaction between lye and water creates plenty of heat on its own.
The “cold” part mainly distinguishes the method from hot process soapmaking, where additional heat is deliberately used to push the soap through saponification more quickly.
With cold process, we mix everything together, pour the raw soap into molds, and let time do much of the work.
And time matters.
A lot.
From Oils to a Bricc
Making a batch of cold process soap isn't terribly complicated on paper.
Doing it well is another matter.
Every oil and fat behaves differently in soap. Coconut oil doesn't contribute the same properties as sunflower oil. Shea butter behaves differently than beef tallow. Castor oil brings something different to the formula than palm oil.
The trick is building a recipe where those ingredients work together.
At Brick Box, our base formula uses a combination of oils, butters, and fats including coconut oil, high-oleic sunflower oil, palm oil, shea butter, castor oil, and beef tallow.
Each has a job to do.
From there, a batch may get ingredients such as clays, coconut milk, sea salt, exfoliants, essential oils, fragrance, or other additions depending on the bricc we're making.
Then comes the part where soapmaking starts looking a little less like cooking and a little more like controlled chaos.
The lye solution and oils are combined and blended until they begin to emulsify and thicken. Soapmakers call this stage trace.
From there, we may divide the batch for different colors, build layers, create swirls, add texture, or keep things intentionally simple.
Then the soap is poured into molds.
But it still isn't ready for your shower.
Not even close.
Why Cold Process Soap Has to Cure
This is one of the biggest differences between handcrafted cold process soap and products designed to move through a factory as quickly as possible.
Cold process soap needs time.
After the soap comes out of the mold and is cut into individual bars, those bars are placed on curing racks and left alone for several weeks.
Saponification largely occurs early in the process, but curing gives excess water time to evaporate and allows the bar to continue developing.
The result is a harder bar that generally lasts longer in the shower and performs better than it would fresh out of the mold.
There's no shortcut we particularly like here.
You can make soap faster.
You can't rush a good cure.
So when a new Brick Box scent is announced weeks before it actually launches, there's usually a reason.
The briccs are back there waiting.
And waiting.
And waiting.
Soapmaking teaches patience whether you want to learn it or not.
Why We Use the Cold Process Method
Could we find an easier way to make soap?
Probably.
Could we find a faster one?
Definitely.
But that's not really the point.
Brick Box started with an interest in traditional soapmaking, and cold process remains at the heart of what we do because it gives us control over the entire bricc—from the oils that go into the pot to the bar that eventually lands in your shower.
It allows us to formulate for the kind of soap we want to make: substantial bars with a rich lather, distinctive ingredients, bold scents, and enough personality that no two briccs need to look exactly alike.
There's also something satisfying about the process itself.
Weigh the oils.
Mix the lye.
Build the batch.
Pour the mold.
Cut the bars.
Put them on the rack.
Wait.
Weeks later, what started as a bucket of oils and fats has become a finished bar of soap.
That's cold process.
Handmade Means Handmade
Around here, “handcrafted” isn't something we slap on a label because it sounds good.
Every batch of Brick Box soap is made in small batches using the cold process method. Every recipe is weighed and mixed here. Every mold is poured here. Every loaf is cut into briccs, cured, inspected, labeled, boxed, and eventually packed into an order.
There are plenty of faster ways to put a bar of something in a shower.
We just happen to like doing it the old-school way.
Because after all the chemistry, measuring, pouring, cutting, curing, and waiting, what you end up with is remarkably simple:
A damn good bar of soap.
Stay wild. Stay clean.
Written by Bill Musall
Founder, Brick Box Natural Soap Company