Superfatting: Why a Little Extra Oil Makes a Big Difference
A Little Extra Goes a Long Way
Have you ever wondered why handmade soap feels more nourishing and moisturizing than commercial bars?
The secret is a little thing called superfatting: a small adjustment that makes a big difference in how your skin feels after every wash.
What Does “Superfatting” Mean?
In simple terms, superfatting means adding a little bit of extra oil or butter to a soap recipe — more than what’s needed to completely react with the lye.
When soap is made, oils and lye (sodium hydroxide) go through a chemical reaction called saponification, which transforms them into soap and glycerin. But if the soapmaker holds back just a bit of lye or adds extra oils, not all of the fats turn into soap. Some stay in their original, skin-loving form.
Those unreacted oils (the superfat) are what make handmade soap feel so rich, creamy, conditioning and gentle instead of drying.
Think of it as the soapmaker’s secret ingredient: a little extra oil for a lot of extra care.
The Chemistry Behind Superfatting
To understand superfatting, it helps to know how chemists figure out exactly how much lye an oil needs in the first place. Different oils , like olive, coconut, or shea butter, each require a different amount of lye to turn into soap. That’s where something called the SAP value comes in.
How Scientists Figure Out SAP Values
At The Clean Chemist, we love a good mystery — especially when it involves soap! One of our favorite detective tools is something called the SAP value, which tells us exactly how much lye an oil or butter needs to turn into soap.
Chemists find the saponification (SAP) value of an oil or butter to learn how much lye it takes to turn that oil into soap. To do this, they mix a small, measured amount of the oil with extra sodium hydroxide (lye). They use more lye than they actually need so they’re sure all of the oil reacts.
After the reaction is done, there’s some lye left over that didn’t get used. The chemist then slowly adds an acid to the mixture until it becomes neutral (not too basic, not too acidic). '
By measuring how much acid it takes to cancel out the leftover lye, they can figure out how much lye was actually used to turn the oil into soap.
That number tells them the SAP value — basically, how much lye is needed to make soap from that specific oil or butter. (source: ISO 3657:2023)
If you aren’t a chemist (or just aren’t in the mood to do detective work), you can find SAP values for
The Soapmaker’s Equation
Once you know the SAP value for an oil, you can calculate exactly how much sodium hydroxide (or lye) is needed to turn it into soap using this simple equation:
Oil Amount in grams x SAP Value = Sodium Hydroxide Needed in grams
For example, if you are using 100 grams of coconut oil and its SAP value is 0.183, the math looks like this:
100 g Coconut Oil x 0.183 = 18.3 g of Sodium Hydroxide
So, to get a 0% superfat soap, the soap maker will use 18.3 grams of sodium hydroxide with 100 grams of coconut oil. But if they want a superfatted soap, the soap maker will intentionally use either a little more coconut oil or a little less sodium hydroxide than shown in the equation.
The result? A soap with leftover oils that nourish your skin.
You Don’t Have to Do the Math Yourself (Unless You Want To!)
Here’s the good news: You don’t have to find SAP values from scratch or do the calculations by hand! Reliable suppliers of oils and butters (like Brambleberry) provide SAP values for each product. This allows soap makers to simply plug their oil amounts into a soap calculator to get a safe and balanced recipe. Cool, right?
Why Superfatting Matters for Your Skin
So, what difference does a little bit of extra oil make for your skin? Quite a bit, actually!
Here’s what superfatted soap does for your skin:
Moisturizing: The leftover oils act like a light lotion, sealing in moisture and leaving skin soft instead of squeaky.
Gentle Cleansing: Superfatted bars clean effectively without stripping away your natural oils.
Creamy lather: Oils like shea butter or castor oil make for a rich, velvety foam.
Custom feel: Different skin types benefit from different levels of superfatting — a bit more for dry skin, a bit less for oily or acne-prone skin.
Finding the Perfect Balance in Soapmaking
The trick to great soap is balance. Too little superfat and your bar can feel harsh. Too much and it may become soft or greasy.
At The Clean Chemist, every recipe is calculated for optimal performance: gentle on skin, long-lasting, and perfectly cleansing.
We test every formula to make sure our superfatted soaps deliver just the right amount of conditioning without sacrificing bubbles or bar firmness.
We use sustainable, conflict-free oils and skin-safe ingredients. Our ingredients are always free from phthalates, parabens, and suspected carcinogens.
