Soap Bar Properties Explained: Hardness, Cleansing, and More

The property numbers a soap calculator shows you (hardness, cleansing, conditioning, bubbly lather, creamy lather, and INS) are predictions built from the fatty acids in your oils. Each one is a sum of fatty acid percentages, weighted by each oil's share of the recipe, and each has a range where finished bars tend to behave well. They aren't measurements of your soap. They're a forecast of how a bar made from those oils will feel, and once you know what each number is made of, you can steer a recipe on purpose. This guide explains what every property in Soaply means, what moves it, and how to read the colored bars when one goes out of range.

How Are Soap Properties Calculated?

Every oil is a mix of fatty acids: lauric, myristic, palmitic, stearic, ricinoleic, oleic, linoleic, and linolenic. Coconut oil is about 48% lauric and 19% myristic. Olive oil is mostly oleic. Castor oil is close to 90% ricinoleic, which no other common oil has in any quantity.

Each property is a sum of particular fatty acids:

For a blend, the calculator weights each oil's fatty acids by its share of the recipe and adds them up, which is why the numbers move predictably when you change a percentage. Coconut oil on its own scores about 67 for cleansing (48 lauric plus 19 myristic). At 25% of a recipe it brings roughly 17 cleansing points with it before the other oils add anything. That one fact explains the usual advice to keep coconut between 20 and 30%: much higher and cleansing runs past the top of the range on coconut alone.

What Does Each Soap Property Mean?

Hardness (29-54 ideal)

What it means: How solid the bar is out of the mold and how well it holds up to daily use in a wet shower.

Affected by:

• Lauric acid (coconut, babassu)
• Myristic acid (coconut, palm kernel)
• Stearic acid (cocoa butter, shea, tallow)
• Palmitic acid (palm, lard, tallow)

Tips:

• Below 29: the bar stays soft, takes days to unmold, and wears away fast
• Above 54: the bar can turn brittle and crack when cut, and it often traces quickly
• Cure time also affects hardness: a low-scoring Castile bar still ends up rock hard after months

Hardness is really two different things sharing a number. Lauric and myristic acid make a bar that's hard but dissolves quickly in water. Palmitic and stearic acid make a bar that's hard and long-lasting. A recipe that reaches 40 hardness on coconut alone won't last as long as one that gets there with tallow or cocoa butter in the mix.

Cleansing (12-22 ideal)

What it means: How aggressively the soap pulls oil off skin. All real soap cleans; this number is about how much of your own skin oil goes down the drain with the dirt.

Affected by:

• Lauric acid (primary contributor)
• Myristic acid

Tips:

• Below 12: the bar can feel like it isn't doing much, especially in hard water
• Above 22: the bar strips natural oils and leaves skin tight and dry
• Balance with conditioning for best results

This is the property most beginners misread. A higher number sounds better, and it isn't. Castile soap scores close to zero here and still gets you clean, because every soap molecule lifts oil. The short-chain soaps from lauric and myristic acid just dissolve oil so well that they don't stop at the dirt.

Conditioning (44-69 ideal)

What it means: How gentle and moisturizing the bar feels after you rinse. It comes from the soaps of unsaturated fatty acids, which are milder on skin.

Affected by:

• Oleic acid (olive, avocado, high-oleic sunflower)
• Linoleic acid (sunflower, hemp, grapeseed)
• Linolenic acid (hemp, flax)

Tips:

• Higher means a milder, more moisturizing feel
• It's the counterweight to cleansing, and the two move in opposite directions as you swap oils
• Above 69, bars tend to be soft and can leave a slight film

Castor oil's ricinoleic acid doesn't count toward conditioning in the calculator. It feeds bubbly and creamy lather instead.

Bubbly Lather (14-46 ideal)

What it means: The volume of big, airy bubbles the bar throws off in the first few seconds.

Affected by:

• Lauric acid (coconut, babassu)
• Ricinoleic acid (castor)

Tips:

• Coconut oil is the bubble king, and babassu is the gentler substitute
• Castor oil stabilizes bubbles so they don't collapse the moment you rinse
• Hard water reduces lather no matter what the number says

Creamy Lather (16-48 ideal)

What it means: Dense, lotion-like lather. Think shaving cream, not dish suds.

Affected by:

• Palmitic acid (palm, lard, tallow)
• Stearic acid (cocoa butter, shea, tallow)
• Ricinoleic acid (castor)

Tips:

• Tallow, lard, and cocoa butter build creamy lather while they build hardness
• It complements bubbly lather rather than competing with it
• Many people prefer a creamy lather for face and shaving bars

INS Value (136-170 ideal)

What it means: A single quality number for the whole recipe, developed by Dr. Robert McDaniel. For each oil, INS is the saponification value (in mg of KOH per gram) minus the iodine value, and the calculator averages those by each oil's share of the recipe.

Tips:

• 136 to 170: well-balanced soap
• Below 136: the bar may be soft or slow to trace, so add saturated fats like coconut or palm
• Above 170: the bar may be hard or brittle and can trace fast, so add liquid oils

INS is a rough summary, not a target to chase. A 100% olive oil bar scores around 105 and has been made for centuries. Use it as a sanity check after the five main properties look right, not as the first thing you balance.

How Do You Read the Property Bars in the Calculator?

When you build a recipe in Soaply, each property shows up as a bar with three things on it: the current value, the ideal range marked in color, and a warning if you're outside it.

Green = Good

The property is inside the ideal range. Nothing to do.

Yellow = Caution

Slightly outside the range. The bar will probably still work, especially if you know why the number is where it is. A Castile recipe sits yellow on hardness and lather by design.

Red = Warning

Far outside the range. Read the warning text, which names the likely problem in plain language ("may be too drying and strip skin's natural oils" when cleansing runs high), and adjust before you mix anything.

The bars update as you type, so the fastest way to learn the properties is to change one oil's percentage by 5 points and watch which bars move. The soap calculator walkthrough covers every input on the page.

Why Do Soap Properties Compete With Each Other?

Properties compete because the same fatty acids feed more than one number, and every point you give one oil is a point taken from another.

Here's what that looks like in practice. Swap 10% of the olive oil in a recipe for coconut oil and cleansing and bubbly lather each climb by about 7 points, hardness climbs too, and conditioning drops by roughly 7. Swap that same 10% to castor instead and bubbly and creamy lather both climb by about 9, cleansing doesn't move, and conditioning drops by the same 7. Same trade on the conditioning side, very different result on the cleansing side.

The other tension is hardness against conditioning, since hardening oils are saturated and conditioning oils aren't. The workaround is to pick hard oils that build hardness through palmitic and stearic acid (cocoa butter, shea, tallow, lard), which don't raise cleansing at all. That's how a bar can be hard, creamy, and mild at once.

What Properties Should Different Soaps Have?

The ideal ranges describe a general-purpose body bar. Once you know what you're making, aim deliberately.

A bar outside the ranges isn't a failed bar, it's one that needs a reason. If you can't name the reason, bring the number back into range.

How Do You Fix a Recipe That's Out of Range?

Too soft (hardness under 29). Raise a hard oil. For a longer-lasting bar, choose palmitic and stearic sources like tallow, lard, cocoa butter, or shea instead of more coconut. A higher lye concentration also helps the bar firm up sooner, though it doesn't change the property number itself.

Too cleansing (over 22). Pull coconut or palm kernel down toward 20% and give the difference to olive, avocado, or rice bran. To keep the bubbles, replace a few points of coconut with castor. Raising the superfat also softens how a high-cleansing bar feels without changing the score, which is why the superfat guide pairs so closely with this one.

Low bubbly lather (under 14). Add castor at 5% first. If that's not enough, add coconut in small steps and watch cleansing.

Thin lather (creamy under 16). Add a butter or an animal fat. Cocoa butter at 5 to 10% makes the lather noticeably denser.

Too conditioning (over 69). Almost always a recipe that's mostly liquid oil. Trade some olive or almond for a hard oil, or accept a softer bar and a longer cure.

Make one change at a time and reread all five bars after each one, since a swap that fixes hardness usually nudges lather and conditioning too. When the numbers land, get the lye and water amounts from the calculator. Never scale lye from another recipe.

What Don't the Numbers Tell You?

Property predictions are estimates based on fatty acid profiles. Several things that change how a bar actually feels don't show up in them at all:

• Cure time. A longer cure makes a harder, milder bar with better lather. The numbers don't change, the soap does.
• Superfat. The properties describe the soap that forms. Superfat is the oil that doesn't, and a higher superfat makes any recipe feel more conditioning than its score suggests.
• Additives. Sugar and honey boost bubbles, salt hardens, clay adds slip, and none of it registers in the fatty acid math.
• Water hardness. Minerals in hard water bind with soap and kill lather. A bar that foams in one town can seem dead in another.
• Fragrance. Some fragrance oils accelerate trace or discolor the bar. That affects the making rather than the finished properties, but it can wreck a batch just the same.
• Oil quality. The fatty acid profile in the database is an average. Olive oil varies by region and harvest, and oil that's started to oxidize behaves differently from fresh.

Use properties as a guide, not gospel. The numbers get you a sensible recipe on the first try. Testing gets you a great one.

Try It Now

Head to the Soaply calculator and experiment with different oils. Watch how adding coconut increases cleansing while olive boosts conditioning, then add 5% castor and see what it does to lather. Finding that balance is the part of soap making that never stops being interesting.

Keep Learning

• Best Oils for Soap Making - Deep dive into each oil's properties
• Complete Guide to Superfat - How superfat affects your bar's feel
• Troubleshooting Failed Batches - Fix common problems

💬 Frequently Asked Questions

What is a good INS value for soap?

The ideal INS value ranges from 136 to 170. Bars in this range tend to be well-balanced with good hardness, lather, and conditioning. Values below 136 may produce soft or sticky bars, while values above 170 can result in hard, drying soap. Treat it as a summary check, since good single-oil soaps like Castile sit outside it.

How do I make my soap bar harder?

Increase the percentage of hard oils like coconut oil, palm oil, cocoa butter, or tallow. You can also use a higher lye concentration to reduce water, which helps bars firm up faster. Adding sodium lactate at 1 tsp per pound of oils also helps.

Why is my soap not lathering well?

Low lather usually means your recipe doesn't have enough lauric acid (from coconut or babassu oil) or ricinoleic acid (from castor oil). Try adding 5-8% castor oil and keeping coconut oil at 20-25% for a good lather boost.

Can soap be too conditioning?

Very high conditioning values (above 70) can mean softer bars that don't last as long and may feel oily rather than clean. If you're selling soap, aim for 44-69 on the conditioning scale for the best customer experience.

Do the property numbers change with superfat or water?

No. Superfat and lye concentration change the lye and water amounts, not the fatty acid math, so the property numbers stay put. Two bars with identical scores can feel different if one has 3% superfat and the other 8%.