If you have read a soap recipe and seen "5% superfat," you have met the single most useful dial in formulation. Here is what it does and how to choose it.
The idea in one sentence
Superfat is the share of your oils you deliberately leave un-saponified — free oil that stays in the finished bar to condition skin and guarantee no leftover lye.
Why you always want some
Saponification values are averages and scales have tolerances. A small superfat (typically 5%) is your safety margin: even if your oils saponify a little more than expected, there is no excess alkali left in the soap.
Choosing a number
- 3–5% — crisp, long-lasting bars; common for high-coconut or salt bars.
- 5–8% — the everyday sweet spot for gentle, skin-friendly soap.
- 8–15% — extra-conditioning, but softer and quicker to turn.
The trade-off
More superfat means more free oil — kinder to skin, but more prone to DOS (the dreaded orange spots) and a softer bar. Cleansing-heavy oils like coconut are usually run at a higher superfat to take the edge off.
Rule of thumb: raise superfat for cleansing-heavy recipes, lower it for gentle, oleic-rich ones.
Set your superfat and watch the lye change live in the saponification calculator.