Isostearic acid is a branched-chain C18 saturated fatty acid (CAS 30399-84-9, C18H36O2, ~284.5 g/mol) used as an emollient and pigment-dispersing agent in cosmetics and as an ester building block for lubricants and metalworking fluids. What makes it valuable to formulators is the methyl branch on its carbon backbone: that single structural quirk keeps the commercial product liquid at room temperature and gives it far better oxidative stability than linear or unsaturated fatty acids of the same chain length. This guide covers what the molecule is, where it earns its place in cosmetic and lubricant formulations, the grade and handling factors that matter when you buy it, and how to source it in bulk.
Table of Contents
- What Isostearic Acid Is
- Cosmetic and Personal-Care Uses
- Lubricant and Metalworking Uses
- Other Intermediate and Surfactant Uses
- Grade, Quality, and Handling
- Isostearic vs. Stearic vs. Oleic Acid
- Frequently Asked Questions
- Source Isostearic Acid in Bulk
What Isostearic Acid Is
Isostearic acid is a saturated 18-carbon fatty acid that carries a methyl branch rather than running as one straight chain. Commercially it is not a single pure compound but a defined mixture of branched C18 isomers, produced by isomerizing oleic or stearic acid over a clay or zeolite catalyst. The chemistry matters because it explains every property a formulator cares about.
A linear fatty acid like stearic acid packs its chains together neatly, so it crystallizes and sits as a hard waxy solid at room temperature. Branching breaks up that packing. Commercial isostearic acid stays a clear, pale-yellow, pourable liquid down to roughly 0 °C, which is why you can meter it straight into an oil phase without melting a wax first. Being saturated, it has essentially no carbon-carbon double bonds — iodine values for good grades typically run below 5 g I2/100 g. That low unsaturation is the source of its standout trait: it resists oxidation, color drift, and rancid odor far better than oleic acid, which oxidizes readily at its double bond.
The practical takeaway: when a formulation needs the spreadability and skin feel of a liquid oil acid but the shelf life of a saturated one, isostearic acid is usually the answer. The trade-off is cost — isomerized branched acids carry a clear premium over commodity stearic or oleic acid, so reserve it for formulations where the liquid state and oxidative stability genuinely pay for themselves.
Cosmetic and Personal-Care Uses
Color cosmetics and skin care are the largest pull for isostearic acid, and the branched structure does three distinct jobs there.
Emollient and skin feel. Swapped in where stearic acid would otherwise sit, it converts a heavy, soapy, occlusive feel into a light, cushioned, non-greasy slip. It conditions the skin surface and reduces tackiness, which is why it shows up in lotions, creams, sunscreens, lip products, and pressed and liquid makeup.
Pigment wetting and dispersion. This is the property color chemists prize most. The branched chain wets the surface of pigments and mineral fillers — iron oxides, titanium dioxide, organic lakes — and keeps them suspended in the oil or solvent phase instead of flocculating. Better dispersion means truer, more saturated color, fewer streaks, and a more stable lipstick, foundation, or mascara. If you have ever fought pigment agglomeration in a color base, isostearic acid (or one of its esters) is a standard tool for fixing it.
Ester feedstock. A large share of isostearic acid never reaches the skin as the free acid at all; it is esterified into derivatives with their own performance profiles. Isopropyl isostearate and isostearyl isostearate are widely used lightweight emollient esters, and pentaerythrityl tetraisostearate delivers a rich cushion with excellent pigment-wetting and spreadability. RawSource carries several of these derivatives alongside the parent acid, so a formulator can source the whole isostearate family from one supplier.
The oxidative stability discussed above carries straight into finished cosmetics: a base built on isostearic acid holds its color and resists rancid odor through a long shelf life, which is exactly what you want in a product that may sit on a shelf for two or three years. Our recommendation for color work specifically — start by trialing isostearic acid as a partial replacement for your existing pigment-grind oil acid and measure gloss and color strength side by side before reformulating the whole base.
Lubricant and Metalworking Uses
On the industrial side, isostearic acid is valued as a stable, liquid building block for synthetic ester lubricants and metalworking fluids. The same branching that helps in a lipstick helps in a gear oil.
Ester base stocks. Reacted with polyols such as trimethylolpropane or pentaerythritol, isostearic acid yields ester base stocks used in greases, lubricants, and metalworking fluids. Esters of branched acids offer high thermal and oxidative stability, good additive solubility, low volatility, and useful low-temperature fluidity — the branch suppresses crystallization so the finished oil pumps in the cold. Because the molecule is saturated and branched, these esters hold up under heat and shear better than oleate-based esters that can oxidize and gum.
Lubricity and corrosion protection. As a polar fatty acid, isostearic acid functions as a boundary lubricity additive, plating onto metal surfaces to cut friction and wear under load. Neutralized with alkanolamines, it forms soaps that provide emulsification, lubrication, and corrosion protection in water-based metalworking fluid concentrates — a single component doing several jobs in the formulation.
Building block for readily biodegradable lubricants. Fatty-acid esters generally show good biodegradability and low aquatic toxicity relative to mineral oils, which is why isostearic acid esters are common in lubricant chemistries developed for environmentally sensitive use. We are careful with that claim: biodegradability is a property of the specific finished ester and must be confirmed by the relevant OECD test on your actual product, not assumed from the raw acid. Treat isostearic acid as an enabling feedstock for those chemistries, then verify the performance and environmental data on the final formulation.
Other Intermediate and Surfactant Uses
Beyond the two flagship markets, isostearic acid is a versatile intermediate. It is the raw material for branched surfactants and emulsifiers — sorbitan isostearate, polyglyceryl isostearates, and isostearamides among them — where the branch delivers stable water-in-oil emulsification and mild, low-irritation performance. It serves as a co-stabilizer and lubricant in polymer and PVC processing, a softener in some rubber and tire compounds, and an additive in textile and leather chemistry. It also goes into soaps and industrial and institutional cleaners, where its stability and dispersancy are the draw.
The common thread across all of these is the same: wherever a process needs a liquid, oxidatively stable, oil-soluble fatty acid that disperses solids well, isostearic acid is a candidate. If you are evaluating it for a new derivative, start from the acid value and iodine value on the certificate of analysis — those two numbers predict most of how it will behave downstream.
Grade, Quality, and Handling
Commercial isostearic acid is sold in grades that differ mainly in purity, color, odor, and isomer distribution. The specifications that drive a buying decision are the acid value (a measure of free-acid content and effective molecular weight), the iodine value (residual unsaturation — lower means better oxidative and color stability), and color (often reported on the APHA/Gardner scale). Cosmetic-grade material is selected for pale color and low odor; a low-odor, low-color grade costs more but is non-negotiable for fragrance-sensitive skin care, whereas an industrial lubricant intermediate can tolerate a darker, higher-odor cut. Match the grade to the application rather than over-buying cosmetic grade for an industrial line.
For handling: isostearic acid is a stable, low-hazard liquid, but it is still a fatty acid and a mild skin and eye irritant, so standard PPE — gloves, goggles, and protective clothing — is appropriate when transferring it. Store it sealed in a cool, dry place out of direct sunlight, ideally around 10–30 °C, to preserve color and prevent moisture pickup. Always work from the supplier’s current Safety Data Sheet and Technical Data Sheet for the exact grade you receive; values vary between producers, and the SDS governs your site handling and disposal procedures.
Isostearic vs. Stearic vs. Oleic Acid
Formulators most often weigh isostearic acid against the two C18 acids it sits between. The table below summarizes why it gets chosen.
| Property | Isostearic acid | Stearic acid | Oleic acid |
|---|---|---|---|
| Structure | Branched C18, saturated | Linear C18, saturated | Linear C18, one double bond |
| State at room temp. | Liquid (pale yellow) | Solid (waxy) | Liquid |
| Oxidative stability | High | High | Low (oxidizes at double bond) |
| Color / odor stability | Excellent | Good | Prone to drift / rancidity |
| Pigment dispersion | Excellent | Moderate | Moderate |
| Skin feel | Light, non-greasy | Heavier, soapy | Light, oily |
| Relative cost | Premium | Commodity | Commodity |
Read across the row that matters to you: isostearic acid is the choice when you want a liquid like oleic acid but the oxidative stability of a saturated acid, and you are willing to pay a premium for it. The next table maps the two main demand sides at a glance.
| Use area | What it does | Typical products |
|---|---|---|
| Cosmetics & personal care | Emollient, pigment wetting/dispersion, ester feedstock, shelf-life stability | Lipstick, foundation, mascara, lotions, creams, sunscreens |
| Lubricants & metalworking | Ester base stock, boundary lubricity, corrosion inhibition (as amine soap) | Synthetic ester oils, greases, metalworking fluid concentrates |
| Other intermediates | Surfactant/emulsifier feedstock, polymer co-stabilizer, softener, cleaner | Sorbitan/polyglyceryl esters, PVC stabilizers, I&I cleaners, soaps |
Frequently Asked Questions
Is isostearic acid a solid or a liquid?
Commercial isostearic acid is a clear, pale-yellow liquid at room temperature and stays pourable down to roughly 0 °C. That is a direct result of its branched structure, which prevents the tight crystal packing that makes straight-chain stearic acid a waxy solid.
How is isostearic acid different from stearic acid?
Both are saturated 18-carbon fatty acids, but stearic acid is linear and isostearic acid is branched. The branch keeps isostearic acid liquid, gives it a lighter and less soapy skin feel, and improves its ability to wet and disperse pigments — at a higher cost than commodity stearic acid.
What is isostearic acid used for in cosmetics?
It works as an emollient that improves skin feel and slip, as a pigment-dispersing agent that keeps color uniform and stable in makeup, and as the feedstock for emollient esters such as isopropyl isostearate, isostearyl isostearate, and pentaerythrityl tetraisostearate. Its oxidative stability also extends finished-product shelf life.
Is isostearic acid safe and how should it be stored?
It is a stable, low-hazard fatty acid but a mild skin and eye irritant, so wear gloves and eye protection when handling it. Store it sealed, cool, and dry, away from direct sunlight, and follow the Safety Data Sheet for your specific grade.
Where can I buy isostearic acid in bulk?
RawSource sources isostearic acid in drums, totes, and IBCs for cosmetic and lubricant manufacturers, and also supplies its common derivatives. Send your grade and volume requirements to request a quote.
Source Isostearic Acid in Bulk
RawSource sources isostearic acid in bulk — drums, totes, and IBCs — for cosmetic and lubricant manufacturers and their purchasing and lab teams. Tell us the grade, specification (acid value, iodine value, color), and volume you need, and we will source it. Request a quote to get started.
