What it means
Soap forms when lye reacts with oils. A recipe with a 0% superfat uses exactly the lye needed to react with all the oil, according to its SAP values. With a superfat, some oil is left unreacted in the finished bar.
There are two ways to get there, and the Handcrafted Soap & Cosmetic Guild separates them:
- Lye discount: work out the lye for your oils, then use a bit less, such as 5% less.
- Superfatting: work out the lye for your oils, then add extra oil, such as 5% more.
Most soap calculators simply ask for a superfat percentage and apply it as a lye discount.
Typical amounts
SoapCalc calls 5% a good balance between safety and performance. SAP values are averages, and the margin guards against leftover lye, which the Guild warns makes soap harsh and even dangerous.
| Superfat | Effect, per SoapCalc |
|---|---|
| 2 to 3% | Harder, more cleansing bar, less conditioning |
| About 5% | Common middle choice |
| 8 to 10% | More conditioning, but softer and less cleansing |
Lye is dangerous to handle, and the amount depends on the exact oils and their weights. Always work out a soap recipe with a lye calculator and follow its safety advice.