Superfatted Soap: What it is and Why we love it!
Superfat for Safety
If you are reading this I'm guessing that you already know that handmade soap is created by blending oils/butters with a caustic alkali ingredient (usually sodium hydroxide -- lye).
The molecules in these combine in a chemical reaction called saponification, and the resulting substance is soap!
So here's where the Superfat for Safety part comes in...
The various oils and butters we use contain different sorts of oil molecules, which require different numbers of lye molecules to turn them into soap. We can use charts or calculators to make sure the numbers work out right, but there are enough variables that getting an exact match is unlikely.
Since we are very likely to have either oil molecules or lye molecules left over after saponification, we just need to decide which is preferable. And since lye is caustic and not nice on skin, that's an easy choice!
When we Superfat, we calculate the amount of lye needed to saponify our oils, then we increase the oils by enough to cover that possible range of variables. 5% is pretty typical, but depending on the oils being used soapmakers may use 10-15% or more.
(I'm not going in to detail on this, but I'll mention that another way of dealing with the variables in oils is called Lye Discounting. This just means that we calculate the amounts of oils and lyes needed and then, instead of increasing the oils, we decrease the lye. Same end result.)
Superfat for Moisturizing
So, we've mixed our oils, lyes, and all the other good things, they've saponified (chemical reaction), and enough hours have passed that all the lye is gone -- changed, along with most of the oils, into soap.
And here's where the moisturizing (or moisture retaining) magic comes in! Because the newly formed soap contains those excess oils, when the soap is used it will have less of an oil stripping effect on your skin than a bar with no extra oils would.
Okay, now maybe you are asking yourself, why don't soap makers use a really Big superfat percentage? Say, 25%? Wouldn't that be awesomely moisturizing?
And the answer is, not really, but it depends!
The right superfat number depends on a range of things, including...
- the recipe used (some oils are more drying than others)
- the desired cleansing level (a "mechanics' soap would need to be more deep cleaning than one intended for delicate skin)
- the soap maker's preferences
Also important is that a high percentage of unsaponified oil will tend to create a softer bar, which might not be desired.
And, finally, unsaponified oils will, generally, reduce a soap's lather. Sad for those of us who like a bubbly bar.
It's All About Balance
So, there you have it!
Superfatting in soap allows for a bar that will leave your skin cleansed but also feeling soft and smooth.
Too little and you risk a harsh, caustic bar, too much and you wind up with a squishy bar that doesn't lather nicely. But thoughtfully judged, considering the recipe's ingredients, you have a soap that cleans gently, lathers delightfully, and leaves skin clean and comfortable.
