A formulator replaces PEG-8 isostearate with PEG-8 diisostearate, expecting a slightly richer oil phase. The emulsion inverts. Nothing else in the formula changed, the INCI names differ by three syllables, and both materials carry roughly the same molecular weight - but the second one has two fatty acids on the chain instead of one, and its HLB is 6.0 rather than 10.0.
That is the whole problem in one sentence. A PEG ester is defined by two independent numbers: the length of the polyethylene glycol chain, and the number of fatty acids esterified onto it. Our PEG ester selection guide walked the first dial - the EO ladder that takes a molecule from water-in-oil emulsifier to solubiliser. This one walks the second, which is harder to buy because it is almost never printed on the label.
Three numbers on the label, two dials underneath
Read PEG-20 Glyceryl Triisostearate as a sentence. "PEG-20" is twenty ethylene oxide units, averaging about 880 g/mol of hydrophilic chain. "Glyceryl" is the glycerol backbone the acids are attached to. "Triisostearate" is three molecules of isostearic acid, about 853 g/mol before the three water molecules split off. Total molecular weight is around 1,770. Three numbers, two of them independent: the EO count and the ester count.
The EO count is the dial everybody turns, because it is in the name and because every supplier publishes an EO ladder. It is also an expensive dial. Going from PEG-8 to PEG-40 stearate adds 32 x 44 = 1,408 g/mol of chain, takes the molecule from a waxy solid to a hard flake, and changes the melt behaviour, the foam, the skin feel and the viscosity of anything it touches.
The ester count does almost none of that. Adding one stearic acid to a PEG monostearate adds 266 g/mol of lipophile, keeps the hydrophilic head identical, and drops HLB by roughly three to four points. If the goal is "same emulsifier, more oil-loving", the ester count is the cheaper dial by a wide margin.
| Dial | What it adds | Effect on HLB | Side effects |
|---|---|---|---|
| EO count (PEG-8 to PEG-40) | About 44 g/mol per unit, all hydrophilic | Up, roughly 0.3-0.4 per unit | Raises melting point, viscosity, foam and cloud point |
| Ester count (mono to di) | About 266 g/mol per C18 acid, all lipophilic | Down, about 3-4 points | Lowers water solubility, raises oil compatibility, can reduce foam |
The eleven grades on our shelf, sorted by ester count
Rows are grouped by the number of ester bonds. The HLB column is the supplier-published figure where one exists and is consistent across sources; the saponification column is calculated from the structure, not copied, so it can be used to audit a certificate of analysis.
| Product | Esters (n) | EO | HLB | SV calculated | Where it earns its place |
|---|---|---|---|---|---|
| PEG-3 Glyceryl Isostearate | 1 | 3 | 6 | 114 | Low-HLB O/W emulsifier; dry-and-wet cleansing oils |
| PEG-10 Isostearate | 1 | 10 | 11 | 79 | O/W emulsifier and solubiliser for creams and lotions |
| PEG-20 Glyceryl Isostearate | 1 | 20 | - | 45 | O/W emulsifier for cleansing oils and sprays |
| PEG-20 Stearate | 1 | 20 | 15.2 | 49 | O/W emulsifier; self-emulsifying base partner |
| PEG-40 Stearate | 1 | 40 | 16.9 | 28 | High-HLB partner, pairs with low-HLB co-emulsifiers |
| PEG-12 Dilaurate | 2 | 12 | 8-10 | 126 | O/W emulsifier and co-emulsifier, creams and bath oils |
| PEG-8 Diisostearate | 2 | 8 | 6 | 127 | W/O emulsifier for cleansing oils, balms, foundations |
| PEG-12 Diisostearate | 2 | 12 | 8 | 106 | O/W-leaning emulsifier, makeup removers |
| PEG-3 Glyceryl Triisostearate | 3 | 3 | 2 | 164 | W/O and anhydrous systems, W/O creams and sun care |
| PEG-20 Glyceryl Triisostearate | 3 | 20 | 8 | 95 | Self-emulsifying core of cleansing oils, 1-20% |
| Sorbiteth-30 Tetraoleate | 4 | 30 | 10.5 | 88 | Cleansing oil and bath oil emulsifier, especially for polar oils |
The saponification column spans 28 to 164 - a factor of nearly six - across eleven products whose names all read "PEG something something-ate". That spread is the ester count talking. It is also the reason a single "PEG ester" specification on a purchase order is meaningless.
Two matched pairs that show the four-point rule
The cleanest evidence comes from pairs where the EO count and the acid are held constant and only the ester count changes. Both pairs below are from the same manufacturer series, so the HLB values are measured by the same method and are directly comparable.
| Pair | Monoester | Diester or triester | Shift |
|---|---|---|---|
| 8 EO, isostearic acid | PEG-8 Isostearate, HLB 10.0 | PEG-8 Diisostearate, HLB 6.0 | -4.0 |
| 3 EO, glycerol backbone, isostearic acid | PEG-3 Glyceryl Isostearate, HLB 6.0 | PEG-3 Glyceryl Triisostearate, HLB 2.0 | -4.0 |
Four points is not a rounding difference. HLB 10 is a comfortable O/W emulsifier for a 20-30% oil phase; HLB 6 is a co-emulsifier for a W/O system, and used alone at 3% in an O/W formula it will produce an unstable, coarse emulsion or invert outright. The same shift appears in the glyceryl triisostearate ladder, where going from 3 EO to 20 EO moves HLB from 2 to 8 - six points for seventeen EO units, at the cost of 750 g/mol of chain and a much higher viscosity. The ester dial delivered four points for 266 g/mol.
One caution before using any published HLB in a formula. Values for the same INCI routinely differ by two units between suppliers, because HLB is measured on an emulsification test and the "average" EO count hides a distribution. PEG-12 dilaurate is published at 8, at 9.7 and at 10 by three different sources; PEG-8 diisostearate appears as 6.0 in the patent literature and as 8.6 in one Chinese catalogue. Compare values only within one manufacturer's series, and treat a cross-supplier difference as a reason to run a bench trial, not as a specification.
Monoesters: the emulsifiers and solubilisers
With one fatty acid and a long EO chain, the molecule is mostly hydrophilic and behaves like a classical non-ionic O/W surfactant. PEG-40 stearate at HLB 16.9 is the high end: it is used at 1-5% as the hydrophilic half of an emulsifier pair, typically with glyceryl stearate, cetearyl alcohol or a low-HLB phosphate ester. Its value is that it is a solid flake with a clean odour, so it can be melted into the oil phase at 70-75 °C without contributing a smell.
PEG-20 stearate at HLB 15.2 sits one step down and is the more forgiving of the two in a cold-process or low-energy system, because it disperses before it dissolves. Both are monoesters, so both carry one free hydroxyl at the end of the PEG chain - the number that later becomes the hydroxyl value on the certificate, and the reason a monoester always shows SV roughly equal to HV.
PEG-10 isostearate at HLB 11 is the branched-chain member of the group. The isostearate tail keeps it liquid at room temperature, which matters in a cleansing milk or a sprayable lotion where a flake raw material would need extra heating and would risk recrystallising on storage.
Diesters: the low-HLB workhorses
Esterify both ends of the PEG chain and the free hydroxyls disappear. Water solubility drops, oil compatibility rises, and the molecule becomes useful exactly where a monoester fails: high-oil systems, cleansing oils and water-in-oil emulsions.
PEG-8 diisostearate at HLB 6 is the reference grade. In published W/O work it appears at 0.5-2% alongside an organically modified hectorite and a low-HLB silicone emulsifier, and the patent data are unambiguous about why both are needed: with the organoclay alone the emulsion separates; with 0.5% PEG-8 diisostearate added, particle stability and appearance stability both come back. At 1% with no low-HLB co-emulsifier the system still fails, which tells you this grade is a bridge between the oil phase and the clay network, not a stand-alone emulsifier.
PEG-12 diisostearate is the same molecule with four more EO units and a published HLB of 8, which moves it from W/O toward O/W. The practical difference in a makeup remover is how fast the emulsion breaks on contact with water: the PEG-12 grade wets out and rinses sooner, the PEG-8 grade leaves a heavier residue that some cleansing balms want.
PEG-12 dilaurate is the short-chain diester, and it is the one to watch on paper. C12 chains pack and melt differently from C18, so the material is a soft solid rather than a liquid, and its HLB is published anywhere from 8 to 10. Its calculated saponification value is 126; one catalogue quotes 102-112 for the same INCI, which back-calculates to an EO count nearer 15 than 12. That is not necessarily an error - dilaurate grades are often blends - but it is exactly the kind of gap that a hydrolysis titration resolves in twenty minutes.
Tri- and tetra-esters: the cleansing-oil core
PEG-20 glyceryl triisostearate is the most commercially important molecule in this article. Three isostearic acids on a glycerol backbone, twenty EO units on the glycerol's remaining hydroxyl, HLB 8, and a viscosity around 300 mPa·s at room temperature despite a molecular weight near 1,770. That combination - high molecular weight, low viscosity, self-emulsifying - is why it is the default emulsifier in Japanese-style cleansing oils at 1-20%, and why it rinses without the tight, squeaky after-feel of a soap-based cleanser.
Its saturated isostearate tails are also the reason it does not yellow. An oleate-based emulsifier at the same HLB will oxidise in the drum and in the bottle; the isostearate version stays water-clear for the shelf life. If a cleansing oil has to be sold in a transparent bottle under retail lighting, this is the grade to specify.
PEG-3 glyceryl triisostearate is the same triester skeleton with almost no hydrophile, HLB 2. It is an oil-phase material, not an emulsifier in its own right: used at 1-5% in W/O creams and anhydrous balms it improves oil miscibility and skin feel, and in a cleansing oil it can trim the overall HLB down to match a paraffin-rich oil blend. Substituting the PEG-20 grade for it will invert the emulsion, because the two differ by six HLB points and 750 g/mol.
Sorbiteth-30 tetraoleate is the four-armed member: a sorbitol core, thirty EO units, four oleic acids, HLB 10.5. Its specialty is polar oils. Rapeseed, olive and ester-based oil blends have a higher required HLB than mineral oil, and this grade is the standard answer in cleansing oils and bath oils built on them. Being a tetraester it also has a high molecular weight, which keeps irritation low and rinse-off feel light, at the cost of a higher iodine value than the isostearates - expect colour drift if the drum is stored warm.
The CAS number cannot see the ester count
Here is where purchasing goes wrong. Polymeric and oligomeric surfactants are registered as families, not as individual grades, so one CAS number covers a whole ladder of EO counts and sometimes a whole ladder of ester counts.
| CAS No. | Grades sharing it | What the number does not tell you |
|---|---|---|
| 68958-56-5 | PEG-8 Diisostearate, PEG-12 Diisostearate; catalogues also list PEG-15 grades under it | The EO count, hence HLB (6 vs 8) and the W/O-to-O/W shift |
| 68958-58-7 | PEG-3 Glyceryl Isostearate, PEG-20 Glyceryl Isostearate; sold elsewhere as PEG-15 and PEG-60 | The EO count, hence SV (114 vs 45) and the entire functional range |
| 86846-21-1 | PEG-3 through PEG-60 Glyceryl Triisostearate | Everything: HLB runs from 2 to 8 across the series |
| 9004-99-3 | PEG-20 Stearate, PEG-40 Stearate | The EO count, hence HLB (15.2 vs 16.9) and melting behaviour |
The ester count is fixed inside each of these names but invisible in the number: 68958-56-5 does not distinguish a monoester from a diester, and neither does 86846-21-1 distinguish a triisostearate from anything else in its family. An order that says "PEG diisostearate, CAS 68958-56-5" is therefore an order for whatever the supplier had in the tank that week. Write the full INCI with the EO number, add the CAS as a cross-check, and add the supplier's own product code as the third lock.
The one certificate figure that can prove the ester count
Saponification value counts ester bonds per gram. Because each ester bond consumes one molecule of KOH, the value scales directly with the number of fatty acids on the molecule and inversely with molecular weight:
SV (mg KOH/g) = n x 56,106 / M, where n is the number of ester groups and M is the molecular weight of the ester.
That single line settles the argument. Work any of the eleven grades and the calculated value lands within a few units of what a genuine certificate shows:
- PEG-20 glyceryl triisostearate: M = 1,772.5, n = 3, so SV = 3 x 56,106 / 1,772.5 = 95. A supplier specification for this exact grade quotes 80-100. Agreement.
- PEG-20 glyceryl isostearate: M = 1,239.6, n = 1, so SV = 45. One Chinese supplier quotes 40-55 for CAS 68958-58-7. Agreement, and the range itself is the tell: 40-55 spans PEG-15 (calculated 55) to PEG-20 (calculated 45).
- PEG-40 stearate: M = 2,028.5, n = 1, so SV = 28. Anything above 35 on a certificate means unreacted stearic acid or a much shorter PEG chain than the label claims.
- PEG-3 glyceryl triisostearate: M = 1,023.6, n = 3, so SV = 164. A "PEG-3 glyceryl triisostearate" arriving with SV 80 is a monoester, not a triester.
Two limits on the method. First, saponification value sees the ester count and the molecular weight together - it cannot separate them. A diester with a short PEG chain and a monoester with a long one can land on the same number; PEG-8 diisostearate computes to 127 and PEG-12 dilaurate to 126, and no titration will tell those two apart. Second, it cannot see the EO distribution at all. Only the hydroxyl value, measured alongside, closes the loop: for a pure monoester HV equals SV; for a di- or triester with no free hydroxyl left, HV collapses toward zero. The ratio SV / HV is, in practice, the ester count.
What to put on the specification
| Parameter | Why it matters | Typical expectation |
|---|---|---|
| Acid value | Residual free fatty acid; high values mean incomplete esterification and odour drift | 5 max for most grades; 15 max for triisostearates |
| Saponification value | The only figure that sees the ester count | Within about 8% of the calculated value above |
| Hydroxyl value | Confirms mono- versus diester, and catches unreacted PEG | Approximately equal to SV for a monoester; near zero for di- and triesters |
| Free PEG | Unreacted chain, a foam and irritation source with no emulsifying value | Ask for the method and the limit; 3% max is common |
| 1,4-Dioxane | Ethoxylation by-product, class 1B carcinogen | 10 ppm per SCCS; 30 mg/kg under China's Safety and Technical Standards |
| Colour, APHA or Gardner | The real difference between an isostearate and an oleate over two years | 50 APHA max for cosmetic isostearates |
| Cloud point or pour point | Confirms the EO count indirectly for liquid grades | State the method; values are not comparable across methods |
Three starting points
- Cleansing oil, 90% oil phase. 82% ester and hydrocarbon oils, 14% PEG-20 glyceryl triisostearate, 3% sorbiteth-30 tetraoleate, 1% water. The PEG-20 triisostearate carries the self-emulsification; the sorbiteth-30 tetraoleate covers the polar fraction of the oil blend. Rinse turbidity should appear within two seconds of adding water - if it does not, the oil blend's required HLB is higher than the emulsifier pair can reach.
- W/O cream, 25% water phase. 0.5-1% PEG-8 diisostearate with 1.5-2% organically modified hectorite and 1-2% of a low-HLB silicone or glyceryl emulsifier. The diester alone will not hold the system; it stabilises the interface between the clay network and the oil.
- O/W lotion, 20% oil phase. 2% PEG-20 stearate as the primary emulsifier with 1% PEG-40 stearate and 1.5% cetearyl alcohol. Two monoesters of the same acid, 1.7 HLB points apart, give a wider process window than a single grade and a better after-feel than a single high-HLB surfactant.
Selection checklist
| If the brief says | Specify | The number to check |
|---|---|---|
| Water-in-oil, 20-30% water, no silicone | PEG-8 Diisostearate or PEG-3 Glyceryl Triisostearate | HLB 6 or 2; SV 127 or 164 |
| Cleansing oil that rinses clear | PEG-20 Glyceryl Triisostearate | HLB 8; SV 80-100 |
| Cleansing oil on a polar oil blend | Sorbiteth-30 Tetraoleate, 2-5% | HLB 10.5; iodine value for colour risk |
| O/W cream, 70 °C process | PEG-40 Stearate as the high-HLB half | HLB 16.9; SV about 28 |
| O/W lotion, cold or low-energy process | PEG-20 Stearate | HLB 15.2; SV about 49 |
| Sprayable or low-viscosity emulsion | PEG-10 Isostearate | HLB 11; SV about 79 |
| Makeup remover, fast rinse | PEG-12 Diisostearate | HLB 8; SV about 106 |
Grades we supply
- PEG-40 Stearate (CAS 9004-99-3) - high-HLB flake emulsifier, 1-5%.
- PEG-20 Stearate (CAS 9004-99-3) - mid-HLB O/W emulsifier, 1-5%.
- PEG-10 Isostearate (CAS 56002-14-3) - liquid O/W emulsifier and solubiliser.
- PEG-12 Dilaurate (CAS 9005-02-1) - diester co-emulsifier for creams, lotions and bath oils.
- PEG-8 Diisostearate (CAS 68958-56-5) - HLB 6 W/O emulsifier for cleansing oils and balms.
- PEG-12 Diisostearate (CAS 68958-56-5) - HLB 8 emulsifier for makeup removers.
- PEG-3 Glyceryl Isostearate (CAS 68958-58-7) - low-HLB O/W emulsifier, dry-and-wet cleansing oils.
- PEG-20 Glyceryl Isostearate (CAS 68958-58-7) - O/W emulsifier for cleansing oils and sprays.
- PEG-3 Glyceryl Triisostearate (CAS 86846-21-1) - HLB 2 oil-phase emulsifier for W/O and anhydrous systems.
- PEG-20 Glyceryl Triisostearate (CAS 86846-21-1) - self-emulsifying core of cleansing oils, 1-20%.
- Sorbiteth-30 Tetraoleate (CAS 63089-86-1) - tetraester emulsifier for cleansing and bath oils.
For the EO side of the same family, see our PEG ester selection guide; for the branched acid that gives these grades their colour stability, see the isostearate ester guide. Send us the oil phase, the required HLB and the process temperature, and we will confirm the grade, the EO number and the certificate figures before the drum ships.