Superfat and water in cold-process soap
Two settings every recipe asks for — and what they actually change about your bar.
Once you understand SAP values, two more dials shape every cold-process recipe: superfat and water. Here's what each one does.
Superfat (lye discount)
Superfat is the percentage of oils you deliberately leave unsaponified. It's the safety margin that keeps a bar from being lye-heavy, and it's where conditioning comes from.
| Superfat | Result |
|---|---|
| 3–5% | Harder, more cleansing, longer-lasting; less margin for error |
| 5–8% | The common all-purpose range — balanced and forgiving |
| 8–15% | Very conditioning (facial / shampoo bars) but softer and shorter-lived; can go rancid sooner |
High-cleansing oils like coconut are often soaped at a higher superfat (or kept to a smaller share of the blend) to avoid a drying bar.
Water — three ways to say the same thing
Water doesn't change how much soap you make; it controls trace speed, cure time, and how the batter behaves. Recipes express it three different ways — they're interchangeable, which trips up a lot of beginners:
- Water as % of oils — the old default (often 38%). Simple, but the actual lye concentration drifts depending on your oils.
- Lye concentration — e.g. "33% lye solution." The most consistent method; the one many experienced soapers prefer.
- Water : lye ratio — e.g. "2:1." Another way to pin the same thing.
Less water = faster trace, harder early bar, shorter cure. A steeper lye concentration (less water) sets up faster and unmolds sooner, but gives you less working time for swirls. More water gives a fluid batter for intricate designs but a softer bar that needs longer to cure.
Cure time
Regardless of water method, cold-process soap needs a 4–6 week cure — not because saponification isn't finished, but because water evaporates, giving a harder, milder, longer-lasting bar. Lower-water recipes can cure a bit faster.
Gear this guide uses
A precise scale and a stick blender are what let you hit superfat and bring batter to trace.
- Weigh oils, lye (NaOH) and water on a 0.1 g digital scale — superfat and lye concentration only hold if your measurements do.
- Bring batter to trace with a stainless immersion stick blender.
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Sources
General guidance — always run your specific recipe through a calculator and wear protective equipment.