What Makes a Soap, a True Soap? The Science Behind TFM
Behind every bar of soap lies a quiet truth — a number that reveals its purity, craftsmanship, and care.
That number is called Total Fatty Matter, or TFM.
At Le Joyau d’Olive, we believe that beauty begins with knowledge.
To understand what you put on your skin is to reclaim a part of yourself.
What Is TFM?
In simple terms, TFM measures how much of your soap is made of true soap: the natural fatty acids and glycerides produced during saponification.
A higher TFM means a richer, creamier bar — one that cleanses gently and nourishes deeply.
A lower TFM often signals a bar filled with moisture, fillers, or synthetic detergents that can strip the skin over time.
Scientifically, TFM is determined through a process defined by ISO 685:2020, the international standard that sets the official method for analyzing soaps.
This method, recognized throughout Europe, quantifies the total alkali content and total fatty matter in a bar — the two main indicators of soap purity and performance.
While ISO 685 does not fix a mandatory percentage, it provides the benchmark by which artisans and laboratories measure quality.
The European Benchmark: Savon de Marseille
In France, the heritage soap known as Savon de Marseille has long embodied the ideal of pure, oil-based soapmaking.
Under its official specification, the bar must contain at least 68 % total fatty acids relative to its final weight — a natural concentration that produces a mild yet effective cleanser.
This requirement, though regional, represents the same principle followed by master soapmakers around the Mediterranean:
that a high proportion of natural oils defines a soap’s gentleness, durability, and authenticity.
Why TFM Matters for Your Skin
A soap rich in fatty matter behaves like skincare, not just cleanser.
It lathers softly, rinses cleanly, and leaves the skin balanced rather than stripped.
People with sensitive skin feel the difference immediately — fewer irritations, no dryness, a subtle suppleness that lingers.
For others, the effect reveals itself gradually: a return to the skin’s natural comfort, as its protective barrier regenerates.
Scientific studies confirm that soaps with higher fatty-acid content retain more glycerol, the natural humectant formed during saponification.
Glycerol helps the skin attract and preserve moisture — a benefit that synthetic detergents, often chemically neutralized, simply cannot replicate.
How to Recognize a True Soap
Not all bars that look like soap are real soap.
Here are a few ways to tell them apart:
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Read the Ingredients
By regulation, ingredients are listed from highest to lowest concentration.
If you see olive oil, coconut oil, sodium palmitate, or sodium olivate among the first few ingredients, you’re holding a genuine soap.
If the list begins with aqua, sodium laureth sulfate, or ingredients you can’t pronounce, it’s likely a synthetic detergent bar. -
Look for Transparency
Brands that follow artisanal or ISO standards often disclose their fatty matter content or describe their saponification method.
Openness about ingredients is always a sign of integrity. -
Listen to Your Skin
True soap leaves the skin calm, soft, and balanced.
If your skin feels tight or dry, it’s telling you that your bar lacks the nourishing oils it deserves.
At Le Joyau d’Olive
Every bar we create is cold-saponified from virgin olive oil and essential oils, then left to mature naturally in vaulted cellars for months.
This slow, ancestral process preserves the natural glycerin that industrial makers often remove — and keeps our fatty matter content exceptionally high around 82%, true to Mediterranean tradition.
Our soaps contain no synthetics, no detergents, and no shortcuts.
They are entirely biodegradable, respectful of the skin, and alive with the quiet richness of pure olive oil.
Because what touches your skin should never be chemistry without soul — it should be nature, perfected by patience.
Breathe Deep
Next time you hold a bar of soap, take a moment to read its ingredients.
Let its origin, its oils, and its simplicity speak for themselves.
That’s where the ritual of cleansing transforms into care.
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Catch the Sunlight, @LeJoyaudOlive