You've dialed in your superfat percentage to 5%. It's sitting on your batch record, maybe even on your ingredient deck: "superfatted for extra moisture." Customers see that and assume higher superfat automatically means a gentler, more nourishing bar.
Here's the uncomfortable part. That number might be telling you almost nothing useful about how your bar actually behaves on hair.
After years of formulating solid haircare, I've landed on a belief that ruffles some feathers: superfat percentage is one of the most misunderstood metrics in this industry. Not because it's irrelevant, but because we borrowed it wholesale from bath soap formulation without stopping to ask whether it actually translates to hair. It doesn't. Not cleanly, anyway.
Where This Number Actually Came From
Superfatting was never designed with hair in mind. The whole concept exists to solve a skin problem. Fully saponified soap is harsh and stripping because there's nothing left behind to cushion the skin barrier. Leave 3-8% of your oils unreacted, and suddenly you've got a bar that cleanses without feeling like sandpaper.
That logic makes total sense for skin. But hair isn't skin, and we tend to forget that.
Hair is dead keratin. There's no living barrier to protect the way there is on skin. When superfat oil lands on a hair shaft, it isn't "nourishing" in any biological sense, it's forming a mechanical film that cuts friction and adds shine. Totally different mechanism, different job entirely. Which means the way we calculate superfat for a body bar shouldn't just get copy-pasted into a shampoo bar formula. Yet that's exactly what most of us are still doing.
Not All Superfat Oil Is Created Equal
Here's something that rarely gets talked about: a 5% superfat of coconut oil and a 5% superfat of high-oleic sunflower oil are not the same ingredient, even though your formulation software logs them identically.
Coconut oil's unsaponified fraction is loaded with lauric and myristic acid, small, highly mobile molecules that don't always distribute evenly across the hair shaft. On fine or already-porous hair, this is often the exact culprit behind that dreaded "waxy buildup" complaint.
Oleic-rich oils tell a different story. Olive oil, high-oleic sunflower, sweet almond, these leave behind a longer-chain, more flexible unsaponified fraction that spreads evenly and behaves much closer to what we'd genuinely call conditioning.
So if your base recipe leans heavily on coconut oil for lather and bar hardness (a completely reasonable choice), you can't treat your superfat the same way you would in an olive-oil-dominant formula. A flat 5% rule slapped across different oil profiles isn't really a formulation strategy. It's a guess with good intentions.
The Iodine Value Nobody's Tracking
Most bar makers measure superfat purely by weight. Almost nobody bothers tracking the iodine value of the superfat fraction specifically, and that's a real blind spot.
Iodine value tells you how unsaturated your oils are. A higher iodine value in your unsaponified fraction leads to a few predictable outcomes:
- Faster oxidation. Rancidity in a finished bar often traces straight back to superfat oil choice, not the saponified portion, which tends to be chemically stable.
- Softer, more spreadable residue on hair. Sometimes that's exactly what you want. Sometimes it's not.
- Different behavior under heat and UV exposure during cure and long-term storage.
Two bars can both claim "6% superfat" on the label and behave in completely different ways on the shelf and on someone's hair, depending on whether that superfat is coming from rice bran oil, castor oil, or cocoa butter.
A practical fix here: calculate a weighted average iodine value for your superfat fraction alone, not your total oil blend. If that number climbs above roughly 70-75, plan on fortifying with an antioxidant (rosemary oleoresin extract at 0.05-0.1% is a solid starting point) and stay conservative with your shelf-life claims, even if the overall bar's iodine value looks perfectly fine on paper.
Why Superfat Should Flex With Hair Porosity
This is the piece of the conversation I think the industry is genuinely missing. Superfat percentage shouldn't be a fixed number baked permanently into your formula. It should flex depending on the hair porosity you're formulating for.
Think about how differently these two hair types respond to the same bar:
- Low porosity hair has a tight, resistant cuticle. A high superfat percentage (7-9%) tends to sit right on top of the shaft instead of absorbing, which is exactly the mechanism behind most "waxy" complaints and negative reviews. This hair type usually does better with 2-4% superfat and lighter oils.
- High porosity or damaged hair, think color-treated, heat-styled, curly or coily textures, has a raised cuticle with more surface area and more gaps for oil to lodge into rather than just coat. This is where 6-8% superfat with smaller, more penetrating oils or esters can actually earn its keep.
Most brands paper over this distinction with marketing language instead of formulation science: "moisturizing" versus "clarifying," pick your lane. That's a real gap in the market, and honestly, a real opportunity. Building a product line where superfat is explicitly calibrated to porosity isn't just smarter formulation, it's a differentiated story that almost nobody else is telling right now.
Are You Formulating on Real Numbers, or Just Theoretical Ones?
One more gap worth naming before we wrap up. Most small and mid-size manufacturers never actually verify their finished bar's real superfat percentage. They lean entirely on theoretical soap-calc numbers based on saponification values, and those values are themselves averages. Averages that shift with natural variation in crop, season, and extraction method, especially with non-fractionated oils.
If you're not periodically titrating finished bars for free fatty acid content, even a basic phenolphthalein titration against KOH will do, you're formulating against paper math that can drift a percentage point or two from what's actually sitting in the bar. That's more than enough drift to push a "balanced" formula into waxy-residue territory without changing a single line of your written recipe.
What This Means for Your Next Batch
Superfat percentage isn't a bad metric. It's just an incomplete one. If you actually want to formulate for hair instead of borrowing skin-soap logic wholesale, here's where I'd put your attention:
- Stop treating superfat as one number. Segment it by the fatty acid profile of the oils involved, not just total weight.
- Track the iodine value of your superfat fraction specifically. It predicts shelf stability and hair feel far better than total percentage alone.
- Calibrate superfat to your target customer's hair porosity. Build this into your product line architecture instead of relying on vague "moisturizing" language.
- Verify with titration. Don't let theoretical SAP-value math be the only thing standing between your formula on paper and your formula in someone's shower.
The next wave of serious solid haircare brands won't win by slapping the highest superfat number they can on a label. They'll win by treating superfat as the multidimensional variable it actually is, one that has to be reasoned through, not just plugged into a soap calculator and forgotten about.