Most cleansing oils that fail in the market fail for one reason: they were bought as an oil, when the job is decided by polarity. Two products can share the same INCI family, the same clear appearance and the same 30 mPa.s viscosity, and still behave nothing alike on waterproof mascara or on a transfer-proof foundation.
The mechanism is solubility. Long-wear makeup and water-resistant sunscreen are built on film formers and silicone resins - trimethylsiloxysilicate, dimethicone crosspolymers, acrylate copolymers - and on oil-soluble UV filters. These dissolve readily in non-polar hydrocarbon and triglyceride phases and barely move in polar ones. Pigments and waxes sit at the other end: they wet out better in a phase that carries some polarity, which is why a completely non-polar oil leaves a grey film of un-wetted pigment on the lashes. No single oil does both jobs, and that is why every workable cleansing oil is a stack of two or three tiers rather than one ingredient chosen by price.
The three tiers, and what each one is paid to do
| Tier | INCI (CAS on our cards) | Behaviour in water | What it dissolves or wets | Typical load |
|---|---|---|---|---|
| Non-polar base | Caprylic/Capric Triglyceride (65381-09-1) | Fully immiscible, floats | Silicone resins, film formers, oil-soluble UV filters | 40-70% |
| Polarity-modified | Caprylic/Capric/Succinic Triglyceride (97708-73-1) | Partially water-miscible, density near 1.0 | UV filters, fragrance, pigment wetting | 10-30% |
| Water-dispersible | PEG-6 / PEG-8 Caprylic/Capric Glycerides (308067-11-0 / 85536-07-8) | Self-emulsifies on contact, turns milky | Fragrance, essential oils, small actives | 5-20% |
| Solubiliser | PEG-40 Hydrogenated Castor Oil, Polysorbate 20 / 80 (9005-64-5 / 9005-65-6) | True solubilisation, clear microemulsion | Essential oils, fragrance, lipophilic actives | 1-8% |
The common commercial mistake is to skip the middle tier. A two-tier oil - cheap triglyceride plus a little PEG glyceride - removes foundation and rinses acceptably, then fails on the two product categories that customers photograph: waterproof mascara and long-wear lipstick. Those are precisely the pigment-plus-film-former combinations that need a phase able to wet pigment and still carry the resin.
Density is the fastest polarity check you can run in the warehouse
Caprylic/Capric Triglyceride sits at 0.94-0.96 g/cm3 at 25 degrees C. The succinic-modified grade is quoted close to 1.0 g/cm3. The succinic acid puts free carboxyl groups onto the molecule, and that is exactly what pulls density and water affinity up while the triglyceride backbone stays the same. Same clear, odourless liquid, same handling, different phase behaviour in the formula.
Practically, this means a supplier who sends a "modified MCT" without a density value has told you nothing. Ask for density at a stated temperature, and for the acid value: the free carboxyls raise it well above the level of a plain MCT, which is usually held at 0.1 mg KOH/g or below. Two drums with the same INCI and different acid values are two different polarities.
The saponification value is still the identity number
Both the plain and the modified product are triglycerides, so the equation used throughout this site still applies: saponification value = 3 x 56,106 / molecular weight. A GTCC reporting SV 325-360 is telling you its average molecular weight is 468-518, which is what a genuine C8/C10 cut looks like. A drum reporting SV near 300 is a heavier cut - average molecular weight around 560 - and it will spread more slowly and feel oilier, whatever the label says.
On the succinic-modified grade the equation stops being a clean identity test, because the succinic acid can be attached as a monoester or bridge two chains, so the ester count n is no longer fixed at 3. That is why the acid value, not the saponification value, is the number to police on this tier: it is the only reading that tracks how much free carboxyl is actually in the drum.
HLB does not travel between suppliers
PEG-6 Caprylic/Capric Glycerides is published at 12.5-14 by one source, 15 by a second and 19 by a third. The spread is not a typo - PEG glycerides are mixtures of mono-, di- and tri-glycerides with a distribution of ethylene oxide units, and each supplier's cut is slightly different. PEG-8 Caprylic/Capric Glycerides is quoted at HLB 17 +/- 1 by the PIT method, with a CMC of 42 mg/L at 25 degrees C and a viscosity of 80-110 mPa.s at 20 degrees C.
The CMC is the more useful number for a formulator. It tells you how much surfactant is needed before micelles form and fragrance actually dissolves; 42 mg/L is very low, which is why this grade solubilises essential oils at a few percent rather than at ten. Compare HLB only inside one supplier's series, and compare CMC across suppliers - the second one is measured, the first one is often calculated from an average structure that no longer exists in the drum.
The skeleton, and the two limits that decide whether it rinses
A workable starting point for a makeup-removing cleansing oil is 60-70% non-polar base, 20-30% polarity-modified triglyceride and 8-12% PEG glyceride. Two limits matter more than the exact split:
- Below about 40% non-polar base, silicone resins stop dissolving and waterproof mascara smears instead of lifting.
- Below about 5% PEG glyceride, the oil does not self-emulsify on contact with water; it leaves a film that the customer removes with a second cleanser and blames on the product.
- Above about 30% polarity-modified triglyceride, rinse-off becomes excellent and makeup removal drops - the oil has become a light lotion.
- Above about 8% solubiliser, the oil turns tacky on the skin before water is added, and the sensory story collapses.
Test it the way the customer will use it
- Apply 1 g to a standardised artificial sebum plus mascara film, massage 30 seconds at 32 degrees C, rinse with 300 ppm hard water at 35 degrees C, then measure residual film gravimetrically or by image analysis. Tap water at 150 ppm will hide a rinse problem that hard water exposes.
- Hold the candidate at 45 degrees C for two weeks and re-run acid value and peroxide value. Triglycerides oxidise quietly; a rising acid value in the drum becomes a rancid note in the bottle.
- Check clarity at 5 degrees C after 24 hours. A polarity-modified triglyceride sitting close to 1.0 g/cm3 is easy to overload, and the oil clouds before it separates.
Purchase checklist
| Reading | Typical value | What it protects you against |
|---|---|---|
| Saponification value | 325-360 (GTCC) | A heavier C12 cut sold as C8/C10 |
| Acid value | 0.1 mg KOH/g max (GTCC) | Hydrolysis in storage; on the succinic grade it is the polarity marker |
| Iodine value | 1.0 g I2/100 g max | Unsaturated carry-over and early oxidation |
| Peroxide value | 1.0 mmol/kg max on receipt | A drum that is already ageing |
| Density at 25 degrees C | 0.94-0.96 vs about 1.0 | Being sold a plain MCT as a modified one |
| Colour and odour | Water-clear, odourless | A off-note that no fragrance will cover in a rinse-off oil |
Selection shortcut
- Waterproof mascara and transfer-proof lipstick: 65-70% non-polar, 20-25% polarity-modified, 8-10% PEG glyceride.
- Daily sunscreen and light makeup: 50/30/20, which rinses faster and feels less heavy.
- A clear micellar-type product rather than an oil: build on the solubiliser tier with PEG-40 Hydrogenated Castor Oil and Polysorbate 20; the triglyceride tiers belong in an oil, not in a transparent water phase.
- Body or baby oil where rinse-off is not the point: non-polar base plus a small amount of polarity-modified grade for pigment or fragrance, and no PEG tier at all.
Supply
We supply the full polarity ladder from one warehouse: Caprylic/Capric Triglyceride (GTCC, CAS 65381-09-1), Caprylic/Capric/Succinic Triglyceride (CAS 97708-73-1), PEG-6 Caprylic/Capric Glycerides (CAS 308067-11-0) and PEG-8 Caprylic/Capric Glycerides (CAS 85536-07-8), with PEG-40 Hydrogenated Castor Oil, Polysorbate 20 (CAS 9005-64-5) and Polysorbate 80 (CAS 9005-65-6) for the solubiliser tier. For the silicone phase that has to be dissolved, Isododecane (and) Dimethicone Crosspolymer is available in the same shipment, and White Mineral Oil 22# (Cosmetic Grade) covers the lowest-cost non-polar end. Cosmetic grades ship with COA showing acid, iodine, peroxide and saponification values; samples of 1 kg are available for bench trials.
For the emulsifier side of the same formula, see our guide to PEG-free polyglyceryl emulsifiers and, for the film formers that make removal hard in the first place, silicone elastomer gel carriers.