Superfat in Soap: What It Is and How Much to Use
Superfat is the oil you deliberately leave unsaponified. Here's what it does and how to choose a number.
On this page
Superfat is the percentage of oils that stays as oil because the recipe uses slightly less lye than needed to saponify all of it. A 5% superfat means 5% of the oils are left free.
Why it matters
Superfat does two jobs. It makes the bar feel milder, and it’s a safety margin: if your scale is off by a gram or an oil’s SAP value varies, there’s still no excess lye.
Typical numbers
| Soap type | Typical superfat |
|---|---|
| Everyday bar | 5% |
| Bars for gifts or sensitive skin | 5–8% |
| Salt bars, 100% coconut | 15–20% |
| Laundry soap | 0–1% |
| Liquid soap (KOH) | 0–3% |
How to set it
Set superfat in the lye calculator. The calculator reduces the lye by that percentage. Don’t add extra oil to a finished recipe to “raise the superfat”; recalculate instead.
FAQ
What is a good superfat for bar soap?
Five percent suits most bar soap recipes.
Does superfat make soap more moisturizing?
It makes the bar feel milder and less stripping. Beyond about 8%, you mostly get a softer bar rather than a noticeably different feel.
Can superfat be too high?
Yes. Above about 8–10% in a normal bar, soap gets softer, lathers less and is more likely to develop orange spots (DOS).
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