A handmade soap quotation is only meaningful if both sides are reading the same numbers. Unlike a plastic component or a machined part, soap does not arrive at a fixed weight and shape — it loses water for weeks after it is made, and its final hardness depends on choices made long before the mould is filled. This is a guide to the numbers that actually decide the bar you receive.
What a Soap Specification Sheet Must State
- Nominal bar weight at the time of packing, plus a tolerance band
- Full ingredient list in descending order of weight
- Saponification values used for the oil blend, and the target superfat percentage
- Water or lye concentration as a percentage of oil weight
- Declared cure time before dispatch
- Fragrance or essential oil load, expressed as a percentage of oil weight
- Batch size for the master sample, so results can be traced
If a quotation omits the third and fourth items, the bar weight you are quoted is not reproducible — it is simply whatever the last batch happened to weigh.
Oil Selection and Saponification Values
Every oil needs a specific amount of sodium hydroxide to convert it into soap. That requirement is expressed as a SAP value — the grams of sodium hydroxide required to saponify one gram of that oil. Values differ between oils because their fatty acid profiles differ, and they differ slightly between published sources, so the supplier's own table always takes precedence over a generic chart.
| Oil | Typical NaOH SAP (g per g oil) | Contribution to the bar |
|---|---|---|
| Coconut | ≈ 0.190 | Hardness and abundant lather; drying if overused |
| Olive | ≈ 0.134 | Gentle, conditioning, slow to harden |
| Palm | ≈ 0.141 | Hardness and stable lather at moderate cost |
| Castor | ≈ 0.128 | Dense, creamy bubbles; sticky above about 10% |
| Shea butter | ≈ 0.128 | Creamy lather and skin feel; can soften the bar |
| Sweet almond | ≈ 0.136 | Light conditioning, good for facial bars |
The arithmetic is straightforward. Multiply the weight of each oil by its SAP value, add the results, then reduce the total by the superfat percentage to get the lye weight. A blend of 1,000 g olive oil and 200 g coconut oil, at 5% superfat, needs roughly:
(1,000 × 0.134) + (200 × 0.190) = 134 + 38 = 172 g NaOH at 0% superfat; then 172 × 0.95 ≈ 163 g NaOH at 5% superfat.
That 9 g difference is the entire margin between a bar that cleans well and a bar that leaves skin tight and reactive.
Superfat: What the Percentage Means
Superfat is the deliberate portion of oil left unsaponified, expressed as a percentage of total oil weight. It functions as a safety margin against measurement error and as a skin-conditioning reserve. Commercial handmade bars generally sit between 3% and 8%. Below 3% there is little protection against small weighing errors; above 8% the bar softens, becomes prone to rancidity, and lathers poorly. A supplier quoting "5% superfat" without also stating the lye concentration is quoting half of a specification.
Water, Cure Loss and the Weight You Will Actually Sell
Water is the ingredient that makes the quoted weight unreliable. A freshly poured bar can contain far more water than the packed bar a month later, and the difference is weight the customer never sees but the invoice does.
| Stage | Typical water content | Commercial implication |
|---|---|---|
| Freshly poured | Highest | Weight at this point is meaningless as a sell weight |
| After 24–48 hours, unmoulded | Still high, surface firm | Cutting stage only |
| After 4 weeks | Most excess water gone | Minimum viable packing point |
| After 6–8 weeks | Stable | Weight now reproducible within a few percent |
The practical consequence: specify the packed weight after a named cure period, and ask what tolerance applies. If the answer is "about 100 g", ask again. A stated range of 95–105 g is a specification; "about 100 g" is not.
Additives That Move the Numbers
- Fragrance oil: typically 3% of oil weight; above about 6% acceleration and seizing become real risks in cold process.
- Essential oils: commonly 1–3%, since many are potent and some, such as cinnamon or clove, accelerate trace sharply.
- Honey, milk or fruit purée: these add sugar, which generates heat in the mould and can discolour or crack the bar; they are easier to control in a milled base than in raw batter.
- Clays and botanical powders: added for colour, they also absorb water and increase the apparent hardness of the cured bar.
Five Checks Before You Sign Off a Sample
- Weigh the sample after 24 hours at ambient conditions and compare it to the stated packed weight.
- Cut one bar in half and inspect for air pockets, uneven colour or a soft centre.
- Wash with it for three consecutive days and note whether skin feels tight afterwards — a reliable indicator of a low superfat.
- Store one bar unwrapped and one wrapped for four weeks, then compare colour, scent strength and surface.
- Confirm the ingredient list on the sample label matches the formulation document exactly, including order.
Moonyoo Biotechnology formulates purely handcrafted, low-temperature soap lines around imported botanical oils, with no unnecessary foaming agents, brighteners, preservatives or stabilizers. Request a sample bar with its full formulation and SAP documentation, and we will supply both.