Superfatting - the superpower of traditional soap making

You'll see the word "superfatted" on a lot of handmade soap labels, including mine. But what does it actually mean, and why should you care?

The short version: it's the percentage of oils in the soap that never got converted into soap. They stay free in the bar and condition your skin while you wash. Every bar of soap from the curated has a superfat — it's one of the main reasons handmade cold process soap feels so different from a standard commercial bar.

How much superfat is in your soap?

Most cold process soaps sit somewhere between 5 and 8%. Here's what that range actually means in practice:

At the curated, I use 5% superfat for decorative soaps with a lot of design work — intricate swirls, layers, and patterns need a batter that behaves predictably, and a slightly lower superfat helps with that. 8% is my standard for most bars. And for the oatmeal soap specifically, I go up to 10% — oat is inherently soothing and I want the bar to reflect that.

One thing worth clearing up: superfat doesn't make a soap better or worse for oily versus dry skin. All properly superfatted cold process soaps are moisturising. Every one of them. The difference between a 5% and an 8% bar is subtle — the 8% feels a touch richer, a touch softer. But both are miles better for your skin than most commercial soaps. Where superfat does matter is in the function of the soap: a shaving soap needs minimal superfat for a slicker lather, while a dish soap for the kitchen needs essentially zero.

Here is a little guidance for superfatting percentages:

0–2%: Dish soaps, shaving soaps, any specialty bar where you need maximum cleansing and the longest possible shelf life. 

3–5%: Decorative soaps with complex designs, or recipes with a high proportion of unstable oils where you want to be conservative. A sensible starting point if you're still learning your formulas. I put here salt soaps as well. Salt soaps tend to “sweat” means collect moisture from the air in humid climates. This moisture can accelerate rancidity, so if you live or sell in humid countries, go low on superfat.

5–8%: The everyday sweet spot. Most bars belong here.

8–12%: When you want a noticeably conditioning bar — oatmeal, shea-heavy recipes, soaps for very dry or sensitive skin. Use stable oils, add vitamin E, and give it time to cure.

Above 12%, rancidity risk climbs fast. Possible to formulate well there, but shelf life will always be shorter and it needs careful oil selection.

How to calculate it

You don't have to calculate superfatting manually — your lye calculator does it for you. In SoapCalc, SoapMaker 3, or Brambleberry's calculator, there's a "lye discount" or "superfat" field. Enter your percentage and the calculator reduces the lye accordingly, creating recipes where that proportion of oils remain unreacted.

Cold process vs hot process: one key difference

In cold process soap, you cannot choose which oils stay free. When lye hits your oil blend, it attacks all oils more or less proportionally. The unsaponified oils in your finished bar are a mix of everything you used — you can't engineer it so that your expensive argan oil is the one that stays free.

Hot process is different. Once saponification is complete — when the batter hits that vaseline-like "applesauce" stage — all the lye has been consumed. At that point you can stir in a luxury oil directly. It won't saponify because there's no active lye left. This is the one case where you genuinely control which oil superfats your soap.

Formulating for higher superfat

If you're working above 8%, you need to be deliberate about rancidity. Free oils in a bar are more vulnerable to oxidation than saponified oils, and the higher the superfat, the faster it can happen.

• Choose oils and butters with long shelf lives for high-superfat recipes. Coconut oil, shea butter, cocoa butter, and mango butter are all stable. Sunflower, hemp, and flaxseed go rancid quickly — I'd keep those at lower percentages or avoid them in high-superfat recipes entirely.

• Add an antioxidant. I use vitamin E (tocopherol) at around 1% of total oil weight. It doesn't stop rancidity forever, but it slows it down meaningfully. ROE (rosemary oleoresin extract) or grapefruit seed extrakt works too.

• Cure properly. A full cure — minimum 4–6 weeks — lets the water fully evaporate and the bar harden and stabilise. High-superfat bars especially benefit from a longer cure. 

Superfatting really is the true superpower of traditional soaps - be it cold or hot processed - as long as you know how to properly formulate the recipe around it!