The oils you choose define your soap. Coconut oil produces hard bars with big lather. Olive makes them conditioning and slow to trace. Castor adds fluffy bubbles. Understanding what each oil contributes — and what its SAP value is — lets you formulate purposefully instead of guessing.
The saponification (SAP) value is the grams of NaOH (or KOH) needed to fully convert 1 gram of an oil into soap. Values vary because each oil has a different fatty acid composition and average molecular weight. FormulaAlchemy uses average SAP values from published literature — actual values vary slightly by crop and supplier, which is why a superfat buffer is always recommended.
Common soap oils at a glance
| Oil | SAP (NaOH) | SAP (KOH) | Hardness | Cleansing | Conditioning | Lather type |
|---|---|---|---|---|---|---|
| Coconut Oil (76°) | 0.190 | 0.268 | High | High | Low | Bubbly |
| Palm Oil | 0.141 | 0.199 | High | Low | Medium | Stable |
| Olive Oil | 0.134 | 0.188 | Low | Low | High | Creamy |
| Castor Oil | 0.128 | 0.180 | Low | Low | High | Fluffy boost |
| Shea Butter | 0.128 | 0.180 | Medium | Low | High | Creamy |
| Cocoa Butter | 0.137 | 0.192 | High | Low | Medium | Stable |
| Lard / Tallow | 0.138 | 0.194 | High | Low | Medium | Creamy |
| Sunflower Oil | 0.134 | 0.188 | Low | Low | High | Creamy |
| Sweet Almond Oil | 0.136 | 0.190 | Low | Low | High | Creamy |
| Avocado Oil | 0.133 | 0.187 | Low | Low | High | Creamy |
| Rice Bran Oil | 0.128 | 0.180 | Low | Low | High | Creamy |
| Hemp Seed Oil | 0.135 | 0.190 | Low | Low | High | Creamy |
| Palm Kernel Oil | 0.178 | 0.250 | High | High | Low | Bubbly |
| Babassu Oil | 0.175 | 0.246 | High | High | Low | Bubbly |
| Canola / Rapeseed | 0.132 | 0.186 | Low | Low | High | Creamy |
| Mango Butter | 0.137 | 0.192 | Medium | Low | High | Stable |
| Neem Oil | 0.136 | 0.190 | Medium | Low | Medium | Stable |
| Jojoba Oil | 0.069 | 0.097 | Low | Low | Very high | — |
| Kokum Butter | 0.135 | 0.190 | High | Low | Medium | Stable |
| Linseed / Flaxseed | 0.135 | 0.190 | Low | Low | High | Creamy |
Key oils in depth
Coconut Oil
The workhorse of soap making. Its high lauric and myristic acid content produces hard bars with excellent, bubbly lather even in hard water. The drawback: it is very cleansing — too much coconut oil strips skin. Most recipes cap it at 25–30% of total oils, with a correspondingly higher superfat.
Olive Oil
Castile soap (100% olive oil) is one of the oldest soap formulations. Olive makes an extremely conditioning bar thanks to its high oleic acid content, but it takes much longer to harden and trace than most oils. Pure olive soap requires a full 6-week cure minimum and will feel slimy or soft until fully cured. In mixed recipes, olive at 40–60% gives conditioning without the slow-trace problem.
Castor Oil
Unique among soap oils due to its very high ricinoleic acid content. Castor does not contribute hardness — it actually softens the bar — but it dramatically boosts lather volume and stability. It also acts as a humectant. Most recipes use 5–10% castor. Above 15%, the bar becomes very soft and sticky during cure.
Shea Butter
Shea's stearic and oleic acid content makes it both mildly hardening and very conditioning. The unsaponifiable fraction in shea (up to 11%) contains compounds that survive saponification and contribute skin-feel benefits. Shea at 10–20% adds a luxurious feel to bar soaps without making them too soft.
Lard and Tallow
Animal fats produce some of the hardest, most stable bar soaps with excellent creamy lather. Their fatty acid profiles closely mirror human sebum, which many formulators believe improves skin compatibility. Tallow at 40–60% with coconut at 20–30% and olive at 10–20% is a classic, reliable formula.
Jojoba Oil (technically a wax)
Jojoba is actually a liquid wax, not a triglyceride oil, and its SAP value is much lower than other oils. It saponifies only partially and its unsaponifiables survive into the finished soap. Jojoba is expensive and usually used at 3–5% for its skin-feel contribution rather than as a bulk oil.
Practical formulation guidelines
- Aim for an INS value of 136–165 for a balanced, hard bar that lathers well. FormulaAlchemy shows this automatically.
- Cleansing score 12–22 is a comfortable range for skin-safe soap. Above 30, the bar gets stripping.
- Conditioning score 44–69 gives a pleasant feel without excessive superfat requirements.
- At least one hard oil at 20–30% (coconut, palm, lard, tallow, cocoa butter) keeps the bar firm enough to use.
- Castor oil at 5–10% almost always improves lather in any recipe. It costs little and the effect is reliable.
- Soft oils (olive, sunflower, canola) above 60% require long cure times — plan for 6–8 weeks minimum.
See how your oil blend scores
Enter your oils in FormulaAlchemy and instantly see hardness, cleansing, conditioning, INS and full fatty acid breakdown — all before you make the soap.