Soap INS Predictor

How It Works

The INS value is a single number that predicts how a soap will perform based on its oil composition. It's calculated from the difference between an oil's saponification value (SAP) and its iodine value (IV):

• INS = SAP value − Iodine value

When you blend multiple oils, the calculator computes a weighted INS based on each oil's percentage. Properties like hardness, cleansing, and lather are derived from the fatty acid profile — the specific percentages of lauric, myristic, palmitic, stearic, oleic, linoleic, and ricinoleic acids contributed by each oil.

How to Use

1. Build your oil recipe — select oils and enter their percentage (must total 100%)
2. Check the INS value — aim for 136-170 for a well-balanced bar
3. Review predicted properties — each property shows a rating (Low, Good, or High) relative to recommended ranges
4. Adjust oils — add or swap oils to bring properties into the "Good" range
5. Export — save your optimized recipe as a PDF

Understanding the Properties

| Property | Ideal Range | What It Means | |----------|-------------|---------------| | Hardness | 29–54 | How firm the bar is; higher = longer lasting | | Cleansing | 12–22 | Ability to strip oils; too high can dry skin | | Conditioning | 44–69 | Moisturizing feel on skin | | Bubbly Lather | 14–46 | Big, fluffy bubbles | | Creamy Lather | 16–48 | Dense, lotion-like foam |

Tips

• Balance hard and soft oils — too many saturated fats (coconut, palm) make a harsh bar; too many unsaturated fats (olive, sunflower) produce a soft, slow-lathering bar.
• Coconut oil above 30% will boost cleansing and bubbles but may irritate sensitive skin. Increase superfat to compensate.
• Castor oil at 5-8% boosts both bubbly and creamy lather without significantly affecting hardness.
• Shea or cocoa butter at 5-15% improves hardness and creamy lather while adding conditioning.

FAQ

What is the ideal INS value for soap?

The ideal range is 136-170. Soaps in this range tend to be hard enough to last, lather well, and feel pleasant on skin. Below 136, bars may be too soft or slow to cure. Above 170, bars may be brittle or overly cleansing.

Can I make soap with an INS outside the ideal range?

Yes — INS is a guideline, not a rule. Many excellent soaps fall slightly outside 136-170. A 100% olive oil soap (Castile) has INS ~109 and makes a wonderfully mild bar, though it takes longer to cure and lathers less.

Why do my percentages need to total 100%?

The predictor uses proportional fatty acid contributions. If percentages don't sum to 100%, the calculations will be skewed — properties will appear lower or higher than they'd actually be in a properly formulated recipe.

How do I improve lather in my soap recipe?

Increase lauric acid (coconut oil) for bubbly lather and stearic acid (cocoa butter, tallow) for creamy lather. Adding 5-8% castor oil boosts both lather types. Keep coconut below 30% to avoid drying skin.

What happens if my INS is below 136?

Soaps below INS 136 tend to be softer, take longer to cure (6-8+ weeks), and may produce less lather. They're not necessarily bad — Castile soap (100% olive, INS ~109) is excellent for sensitive skin but needs patience.

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Last reviewed: June 2026