Understanding Superfat in Artisan Soap: The 5% That Changes Everything

If you've ever fallen in love with a handmade soap that feels especially silky and kind to your skin, there's a good chance one quiet decision made the difference: the superfat level.

Behind the scenes, every cold process recipe balances oils, lye, and water. Superfat is the part of that balance that most customers never see but feel every time they wash. It's what turns a basic cleansing bar into something that feels cushioned, comforting, and just that little bit more forgiving for dry or sensitive skin.

In this guide, I'll explain what superfat actually is, why a modest 5% superfat can change how a bar feels on your skin, and how I use it in The Humble Shepherd studio to create soaps that cleanse thoroughly without being unkind.

What Is Superfat in Handmade Soap?

In simple terms, superfat is the extra oil left unsaponified in a finished bar of soap.

During saponification, lye (sodium hydroxide) reacts with oils and converts them into soap. If you calculate your recipe so that there is exactly enough lye to turn every drop of oil into soap, you have a 0% superfat bar. But most artisan soap makers deliberately use slightly less lye than the mathematical maximum, leaving a small amount of oil unreacted.

Several technical guides describe it in almost identical terms. The team at Classic Bells define superfat as "any excess fat that remains in a soap after saponification is done" in their explanation of superfat in soap making. UK supplier The Soapery describes superfat as "an excess of butters and oils in a finished bar of soap that have not been saponified" in their guide to what superfat means in cold process recipes.

In practice, that means if I superfat a recipe at 5%, about five percent of the oils remain in their original, skin-loving form in the finished bar. They sit alongside the cleansing soap molecules, softening the overall feel.

Why Do Artisan Soap Makers Use Superfat?

There are three main reasons I build superfat into almost every bar at The Humble Shepherd.

1. Skin Comfort and Mildness

A modest superfat gives your skin a cushion of extra oils during washing. Makers like Bramble Berry, in their guide to superfatting soap and how it affects skin feel, note that a 5% superfat is often enough to make a bar feel more luxurious and moisturising without making it too soft.

That lines up with what my customers tell me. Bars with a thoughtful superfat tend to leave skin feeling less tight after washing, pair beautifully with a moisturiser afterwards, and work especially well for those who've previously found commercial soaps too "squeaky" or drying.

If you're curious how this connects to moisture, our deep-dive on glycerin in handmade soap and why it stays in cold process bars explores how natural humectants and superfat together support more comfortable cleansing.

2. Safety Margin Against Lye-Heavy Soap

No matter how careful we are, ingredients can vary slightly and kitchen scales are never absolutely perfect. A small superfat acts like a safety cushion. Classic Bells highlight this in their explanation of why superfat helps protect against small measurement errors, and soapers in community discussions often recommend 3 to 5% for beginners to reduce the risk of accidentally lye-heavy bars.

It means that even if a bottle of oil is a touch different from its stated saponification value, or if we're out by a fraction of a gram on the scales, there's still a little extra fat left over in the finished bar, rather than stray lye.

3. Recipe Personality and Skin Type

Superfat also helps shape the character of a bar. A high-olive "Castile-style" soap with a cosy 7 to 8% superfat might feel very mild and creamy, ideal for dry or mature skin. A brisk, cleansing kitchen or gardener's bar might lean closer to 3 to 5%, focusing more on effective degreasing.

In more advanced formulations, some makers even target certain oils to remain as the superfat, a technique explained in Seawitch Botanicals' article on balancing saponification and superfat for gentler bars.

In my workshop, I rarely go to extremes. For The Humble Shepherd's everyday body bars, 5% is the quiet hero that keeps things balanced.

How Much Superfat Is "Best"?

There's no one perfect number, but there are sensible ranges.

Guides for home and professional makers often recommend 3 to 5% for everyday body bars, 5 to 8% for drier skin or more conditioning bars, and higher numbers only for very specific applications, as they can cause issues.

Bramble Berry, for example, recommend a 5% superfat as a good default, noting that it adds noticeable luxury "without making it too soft or inhibiting lather" in their piece on how to choose superfat percentages.

Classic Bells point out that very high superfat levels can cause soft, squishy bars, increased risk of rancidity or "Dreaded Orange Spots", and poor lather that feels oily rather than creamy.

For The Humble Shepherd, most bars sit at 5%, specially conditioning recipes may go a touch higher, and heavily cleansing or exfoliating bars tend to stay in the 3 to 5% range to balance rinse-off.

If you want to see how this plays out on your skin, our guide to choosing moisturising bar soaps and the key ingredients to look for is a natural next step.

Superfat, pH, and the Skin Barrier

Superfat does not lower a bar's pH into the skin's natural range. Properly made soap still has a pH around 9 to 10. However, it does influence how that bar behaves on the skin.

Research into the acid mantle shows that healthy skin typically sits between pH 4.5 and 5.5, and that this slightly acidic surface plays an important role in barrier function and microbiome balance. A recent review in the Journal of Investigative Dermatology summarises how an acidic pH helps regulate the microbiome and structural stability of the skin.

Other work on cleansers and the acid mantle shows that even mildly alkaline products can temporarily raise skin pH, but that gentle formulations and appropriate moisturising afterwards help the barrier to recover.

For me, superfat is one of the tools alongside thoughtful choice of oils, simple fragrance levels, and a full 4 to 6 week cure that help a traditional soap bar behave as kindly as possible: less stripping of surface lipids, a softer, more cushioned skin feel, and a better partnership with your chosen moisturiser or emollient.

If you're navigating dry or sensitive skin, our overview on discovering the best soap bars for sensitive skin puts superfat into a broader context of ingredients, fragrance, and routine.

How Superfat Affects Lather and Longevity

Superfat isn't just about skin feel; it also quietly influences how your bar behaves in the bathroom.

Higher superfat (within reason) gives creamier, more cushioned lather but slightly faster use-up, because more of the bar is oil rather than pure soap. Lower superfat creates firmer, longer-lasting bars with crisper, more "bubbly" lather but potentially less cushioning.

This is where cure time makes a big difference too. A high-superfat bar that's under-cured might feel sticky and soft. The same bar, cured properly for 4 to 6 weeks (or more, for high-olive recipes), can feel silky and luxurious instead of greasy. If you're interested in that side of things, our piece on why cold process soap takes 4 to 6 weeks to mature properly walks through what's happening on the curing rack.

How I Use Superfat at The Humble Shepherd

In my own recipes, superfat is a quiet design decision I make long before the batch hits the mould.

When I'm formulating a bar, I think about who it's for. Drier, more mature or winter-parched skin? I'll favour 5 to 7%. A gardener's or exfoliating bar? I'll lean closer to 3 to 5%.

I think about what role it plays in the routine. A main daily body bar should sit in that gentle, balanced 5% sweet spot. A facial bar may combine a modest superfat with specific oils (like jojoba or rice bran) that mirror skin's natural lipids.

I think about what oils are included. Some oils, like shea butter and avocado oil, feel extra comforting when they form part of the superfat. Others, like coconut oil, need to be used carefully to avoid becoming too stripping at higher percentages.

If you're curious about how these choices show up in real life, our guide to winter skin rescue and handmade soaps for cold weather comfort explains how I adapt superfat and ingredients to support skin when the heating comes on and the air gets dry.

FAQs: Superfat in Artisan Soap

1. Does more superfat always mean a better soap?

Not necessarily. While a moderate superfat (around 5%) usually improves skin feel, too much can make bars soft and prone to going mushy, reduce lather significantly, and increase the risk of rancidity over time. The aim is balance, not excess.

2. Does superfat make soap safe for very dry or eczema-prone skin?

Superfat can make a bar gentler and more forgiving, but handmade soap is still soap. It's not a replacement for medical emollients. NHS guidance for dry skin often recommends emollient cleansers or leave-on emollients instead of regular soap for people with diagnosed dry-skin conditions.

If you have eczema or another skin condition, it's always best to follow your clinician's advice first and treat gentle, superfatted soaps as a complementary choice rather than a treatment.

3. Is superfat the same as moisturiser?

No. Superfat adds free oils to the bar, which can cushion the skin during washing and reduce the stripping effect, but it's not the same as applying a leave-on moisturiser. For lasting hydration, pairing a gentle bar with a good emollient or cream afterwards is still important, especially in winter.

4. Can I feel the difference between 3% and 5% superfat?

Many people can. A 5% superfat bar often feels a little more "cushioned" and silky, whereas 3% can feel slightly crisper and more rinsing. But oil choice, cure time, and fragrance level all interact with superfat, so it's the full recipe that you're really feeling.

Want to Experience a Thoughtfully Superfatted Bar?

Every bar at The Humble Shepherd Co. is formulated with a carefully chosen superfat level that balances comfort, lather, and longevity.

If you'd like to feel the difference a well-superfatted, fully cured bar can make in your own routine, you can browse our handmade soap collection and explore ingredient-led stories in posts like moisturising bar soap and the best ingredients to look for.

And to make sure you don't miss new batches as they come off the curing rack, you can join our Shop Now waitlist and be first to know when fresh bars are ready.