Superfat in Soap Making: What Percentage Should You Use?
Learn what superfat means, how it reduces calculated lye, and what to consider when choosing a superfat percentage for a soap recipe.
What superfat means
Superfat is a deliberate reduction in the lye used to saponify a recipe. A 5% superfat does not simply mean adding 5% more oil at the end; in a calculator, it means using less lye than the theoretical amount required for complete saponification.
Choosing a percentage
Many bar soap recipes begin around 5%, but there is no universal best value. The oil blend, cleansing profile, intended use, process, and measurement accuracy all matter. A higher setting increases the lye discount, but it can also affect hardness, lather, shelf life, and the amount of unsaponified material.
Calculate it with the complete recipe
Set superfat before calculating so it is applied to every oil through its SAP value. Avoid adjusting the final lye number by hand unless you fully understand the calculation basis and the purity of the alkali being used.