Ask three suppliers for neopentyl glycol diheptanoate (CAS 68855-18-5) and the datasheets will agree on the CAS number and disagree on almost everything else: one quotes 12-15 mPa.s at 25 °C, another 12-18 cSt, a third only a lubricant-grade figure at 40 °C. The reason is that an emollient ester is not a single substance. It is the product of three decisions - which polyol core, which fatty acid, and how completely you push the esterification - and only the first of those is visible in the INCI name. This guide covers the five polyol cores behind almost every commercial emollient ester, shows how two laboratory numbers let you identify what is actually in the drum, and builds a viscosity ladder you can use to place an ester before you ever open a sample.
Five cores, five architectures
Every polyol ester begins with an alcohol carrying two or more hydroxyl groups, esterified with a fatty acid. The core fixes how many ester arms the finished molecule carries, and that count - more than the acid - decides how the molecule behaves on skin.
| Polyol core | Formula | Molecular weight | Hydroxyl groups | Ester arms when fully capped | What the core contributes |
|---|---|---|---|---|---|
| Propylene Glycol | C3H8O2 | 76.09 | 2 | Diester | Smallest and most polar core; lightest, driest oils of the family |
| Neopentyl Glycol (NPG) | C5H12O2 | 104.15 | 2 | Diester | Two shielded hydroxyls; fast-spreading, very low-viscosity esters |
| Trimethylolpropane (TMP) | C6H14O3 | 134.17 | 3 | Triester | Three arms over three carbons; silky, dry oil with a longer play time |
| Pentaerythritol (PE) | C5H12O4 | 136.15 | 4 | Tetraester | Four arms from one central carbon; the pigment and cushion core |
| Dipentaerythritol | C10H22O7 | 254.28 | 6 | Hexaester | Two cores linked by an ether bond; the heaviest, most substantive esters |
The neopentyl core is why this family exists at all. In neopentyl glycol, trimethylolpropane, pentaerythritol and dipentaerythritol the carbon carrying the hydroxyls also carries two or three methyl groups, so every ester bond sits next to a sterically shielded quaternary carbon and hydrolyses slowly. That shielding is the whole point: it is what keeps these esters intact at the pH values and temperatures where a glyceride or a straight-chain alkyl ester would already be splitting. Propylene glycol gives up the shield and gains polarity; dipentaerythritol keeps the shield and doubles the arm count.
Two numbers that identify what you bought
Saponification value (SV, mg KOH/g) counts ester bonds. It is the mass of potassium hydroxide needed to hydrolyse one gram of ester, and for a fully esterified polyol it follows directly from the structure:
SV = 56,106 x n / M, where n is the number of ester groups and M is the molecular weight of the ester.
Because each esterification consumes one hydroxyl and one carboxyl group and releases one molecule of water, the molecular weight is just as predictable:
M = M(polyol) + the sum of the acid molecular weights - 18.015 x n
Put the two equations together and you can predict the saponification value of any polyol ester worth selling, without a laboratory. The table below does it for the products on this page; every calculated molecular weight matches the formula printed on the product card, and where a supplier band is available it is shown alongside.
| Product (CAS) | Polyol / acid | Formula | Ester MW (calculated) | SV predicted from MW | SV on supplier COA |
|---|---|---|---|---|---|
| Propylene Glycol Diethylhexanoate (93981-97-6) | PG / branched C8 | C19H36O4 | 328.5 | 342 | - |
| Neopentyl Glycol Diheptanoate (68855-18-5) | NPG / linear C7 | C19H36O4 | 328.5 | 342 | - |
| Neopentyl Glycol Diethylhexanoate (28510-23-8) | NPG / branched C8 | C21H40O4 | 356.5 | 315 | 275-305 |
| Neopentyl Glycol Dicaprylate/Dicaprate (70693-32-2) | NPG / C8-C10 blend | Mixture | 356-413 | 272-315 | - |
| Propylene Glycol Dicaprylate/Dicaprate (58748-27-9) | PG / C8-C10 blend | Mixture | 328-385 | 292-342 | - |
| Trimethylolpropane Triethylhexanoate (26086-33-9) | TMP / branched C8 | C30H56O6 | 512.8 | 328 | - |
| Trimethylolpropane Tricaprylate/Tricaprate (11138-60-6) | TMP / C8-C10 blend | Mixture | 513-597 | 282-328 | - |
| Trimethylolpropane Triisostearate (68541-50-4) | TMP / branched C18 | C60H116O6 | 933.6 | 180 | - |
| Pentaerythrityl Tetraisononanoate (93803-89-5) | PE / branched C9 | C41H76O8 | 697.0 | 322 | - |
| Pentaerythrityl Tetracaprylate/Caprate (68441-68-9) | PE / C8-C10 blend | Mixture | 641-753 | 298-350 | - |
| Dipentaerythrityl Pentaisononanoate (84418-63-3) | di-PE / 5 x branched C9 | Mixture | 955.4 | 294 | 290-310 |
| Dipentaerythrityl Hexacaprylate/Hexacaprate (68130-24-5) | di-PE / 6 x C8-C10 | Mixture | 1011-1180 | 285-333 | 305-325 |
Two conclusions fall out of that table, and both are useful at the purchasing desk.
- Saponification value identifies the acid, not the polyol. Within one acid family the polyol barely moves the number. Esterify caprylic acid (C8) with propylene glycol, neopentyl glycol, trimethylolpropane, pentaerythritol or dipentaerythritol and the predicted values are 342, 315, 328, 350 and 333 - a spread of about 35 units across five completely different architectures. Change the acid from caprylic to capric and every one of them falls by 40-60 units. Move to isostearic acid and trimethylolpropane triisostearate drops all the way to 180. A certificate reading "SV 320" therefore tells you the acid fraction is short and the ester is fully capped. It tells you nothing at all about which polyol you were sold. If the polyol carries your texture claim, specify the INCI, not a saponification window.
- Hydroxyl value reveals how completely the ester was capped. A fully esterified polyol ester has no hydroxyl left, so its hydroxyl value should be close to zero - and the trade datasheets confirm it: Dipentaerythrityl Hexacaprylate/Hexacaprate (68130-24-5) is quoted at a hydroxyl value of 5 mg KOH/g maximum. Its partially esterified relative, Dipentaerythrityl Pentaisononanoate (84418-63-3), carries five ester arms on a six-hydroxyl core and is quoted at 30-70 mg KOH/g. Run the arithmetic backwards and one free hydroxyl on that 955 g/mol molecule predicts 56,106 / 955 = 59 mg KOH/g - squarely inside the supplier band. That is not a coincidence, it is the specification. The free hydroxyl is deliberate: it is what pulls the molecule towards the water side of the interface and turns a light emollient into a co-emulsifier and film-former.
The same arithmetic predicts the saponification values those two products actually carry. The pentaisononanoate should read 294 mg KOH/g and suppliers quote 290-310. The C8/C10 hexaester should read between 285 and 333 depending on the caprylic-to-capric ratio, and suppliers quote 305-325. When a calculated figure and a published band agree that closely, the calculation becomes a receiving-inspection tool: a lot whose measured SV falls outside the band was esterified with the wrong acid fraction, whatever the label says. One honest footnote - the neopentyl glycol diethylhexanoate band of 275-305 sits a little below the 315 that pure 2-ethylhexanoic acid predicts, which is the normal signature of a technical grade carrying a small heavier-acid tail.
The viscosity ladder: 10 mPa.s to 2,800 cPs
Molecular weight sets viscosity, the polyol sets molecular weight, and within one family that relationship spans nearly three orders of magnitude.
| Product (CAS) | Ester MW | Published viscosity | Skin-feel position |
|---|---|---|---|
| Neopentyl Glycol Diethylhexanoate (28510-23-8) | 356.5 | 9.5-13.5 mPa.s at 25 °C | Lightest rung; fresh, non-greasy, silicone-like glide |
| Neopentyl Glycol Diheptanoate (68855-18-5) | 328.5 | 12-15 mPa.s at 25 °C | Very fast spreading, dry matte finish, no volatile |
| Pentaerythrityl Tetracaprylate/Caprate (68441-68-9) | 641-753 | 28-34 cPs, 50 cSt, and 67-74 mm2/s at 20 °C across three suppliers | Medium body with strong pigment affinity |
| Dipentaerythrityl Hexacaprylate/Hexacaprate (68130-24-5) | 1011-1180 | 70-150 mm2/s at 40 °C | Substantive, slightly oily, mineral-oil-like cushion |
| Dipentaerythrityl Pentaisononanoate (84418-63-3) | 955.4 | About 2,800 cPs at 25 °C | Heaviest rung; tacky film-former and gloss builder |
Two cautions when reading a viscosity figure. First, temperature and units must both be stated: 12 mPa.s at 25 °C and 12 mm2/s at 40 °C are not the same fluid, and suppliers move between the two conventions freely. Second, the same INCI can legitimately ship at very different viscosities - pentaerythrityl tetracaprylate/caprate is published by three suppliers at 28-34 cPs, at 50 cSt and at 67-74 mm2/s, a spread of roughly 2.5 times. That is not a misprint; it reflects the caprylic-to-capric ratio in the acid feed. Specifying the INCI alone leaves that swing open. Put a viscosity band, with temperature and method, on the purchase order.
Branching versus linearity: same formula, different fluid
The most useful structural comparison in this family costs nothing to check, because it is pure arithmetic. Two pairs on this page are isomers:
- Propylene Glycol Diethylhexanoate (93981-97-6) and Neopentyl Glycol Diheptanoate (68855-18-5) are both C19H36O4 at 328.5 g/mol, and both therefore carry a theoretical saponification value of 342. One is a propylene glycol diester of a branched C8 acid; the other a neopentyl glycol diester of a linear C7 acid. A saponification value cannot tell them apart. Only the core and the chain shape do.
- Neopentyl Glycol Diethylhexanoate (28510-23-8) and the caprylate member of Neopentyl Glycol Dicaprylate/Dicaprate (70693-32-2) share the formula C21H40O4 at 356.5 g/mol and the same theoretical SV of 315 - one built from a methyl-branched C8 acid, the other from a linear C8 acid. The branched version is quoted at 9.5-13.5 mPa.s at 25 °C; the linear acid packs better, so it crystallises more readily and reads as more body at the same molecular weight. Trimethylolpropane Triethylhexanoate (26086-33-9) and the caprylate member of Trimethylolpropane Tricaprylate/Tricaprate (11138-60-6) are the same story one rung up: both are C30H56O6 at 512.8 g/mol.
The practical reading is that branching on the acid side buys you fluidity at a given molecular weight, and linearity buys you structure. If a formula hazes in a cold warehouse or a stick goes soft in summer, the acid geometry - not the ester's molecular weight - is the first thing to check.
Matching the ester to the job
- Light, dry, and a replacement for volatile silicones - Neopentyl Glycol Diheptanoate (68855-18-5). C19H36O4, 328.5 g/mol, 12-15 mPa.s at 25 °C. Its commercial reputation rests on two claims worth understanding rather than repeating. It is non-volatile, so it reproduces the dry, fast-spreading afterfeel associated with cyclomethicone without the VOC question. And it is an unusually good solvent for organic UV filters - trade literature positions it as superior to C12-15 alkyl benzoate for solubilising sunscreen actives, which matters because a filter that crystallises during shelf life is an SPF failure, not a texture failure. Use it in the oil phase at 2-8 % in light emulsions and lotions and 10-20 % in a high-SPF sunscreen where the filter load is what stresses the solvent. Its C7 chain is short, so where the formula also needs a lingering emollient afterfeel, pair it with a medium-viscosity ester from lower down this page.
- Minimum viscosity and a silicone-like glide - Neopentyl Glycol Diethylhexanoate (28510-23-8). C21H40O4, 356.5 g/mol, 9.5-13.5 mPa.s at 25 °C, saponification value 275-305, acid value 0.1 maximum, hydroxyl value 5 maximum, refractive index 1.425-1.455 at 20 °C. The branched acid keeps it fluid and gives a dry, slippery draw that reads as silicone to the finger. Makeup, powder, sunscreen and any skin-care brief where "fresh and non-tacky" is written down. This is the ester to reach for when a heavier ester is making a lotion drag.
- Medium body and pigment carrying - Pentaerythrityl Tetracaprylate/Caprate (68441-68-9). The tetraester of mixed caprylic and capric acids, calculated SV 298-350, typical acid value 0.3 maximum, density around 0.95-0.96. It is the workhorse of the middle rung: an emollient, a low-viscosity spreading agent and a pigment carrier in one. Foundations, primers, SPF colour cosmetics and acne-prone formulas all use it because it spreads pigment evenly without the heavy occlusive film that a mineral oil or petrolatum would leave. Pentaerythrityl Tetracocoate (92201-72-4) is the same tetraester architecture built on a coconut fatty acid blend - different acid distribution, same calculated SV band, and the sensible choice when the acid profile rather than the architecture is what the brief specifies.
- Gloss and cushion - Pentaerythrityl Tetraisononanoate (93803-89-5). C41H76O8, calculated molecular weight 697.0, density 0.953 at 20 °C, calculated SV 322, reported viscosity around 120-150 mPa.s at 25 °C. The branched C9 acid keeps a 697 g/mol tetraester pourable at room temperature while the four arms give it gloss and staying power: skin creams, lotions, colour cosmetics and lip products where a glossy finish is the point. It sits above the C8/C10 tetraester on the viscosity ladder for the same calculated acid fraction, purely because isononanoic acid is heavier than caprylic acid.
- Substantive, mineral-oil-like cushion - Dipentaerythrityl Hexacaprylate/Hexacaprate (68130-24-5). The six-armed hexaester, calculated SV 285-333 against a supplier band of 305-325, acid value 0.5 maximum, hydroxyl value 5 maximum, iodine value 1 maximum, viscosity 70-150 mm2/s at 40 °C. Trade descriptions place it as a medium-to-heavy, odourless emollient with a soft and slightly oily afterfeel - the sensory profile of a light mineral oil with the oxidative stability of a neopentyl polyol ester. Lipstick, lip balm, stick products and rich creams, where its high flash point and low volatility also protect the batch during a hot pour.
- Film formation and silicone substitution - Dipentaerythrityl Pentaisononanoate (84418-63-3). Five ester arms, one free hydroxyl, and that single hydroxyl is the reason the product exists. Hydroxyl value 30-70 against a calculated 59, saponification value 290-310, about 2,800 cPs at 25 °C, colour APHA 50 maximum, decomposition temperature around 300 °C. The remaining hydroxyl makes it a co-emulsifier and a film-former at once, which is why it improves gloss, fullness, wear resistance and pay-off in lipsticks and lip oils, and why around 0.5 % of it substitutes for silicone in hair care. It is the highest-viscosity rung of the ladder, and the one where hydroxyl value is not a quality flag but a design parameter.
- Water-side polarity - Propylene Glycol Dicaprylate/Dicaprate (58748-27-9) and Propylene Glycol Diethylhexanoate (93981-97-6). Built on the 76.09 g/mol diol core with no neopentyl shield, these are the smallest and most polar esters in the family. Propylene Glycol Dicaprylate/Dicaprate is the classic light dry oil for skin, sun and makeup; Propylene Glycol Diethylhexanoate, C19H36O4 at 328.5 g/mol, is positioned in bath, cleansing and hair-care systems where the ester has to tolerate a higher water content than a pure oil-phase emollient would.
The certificate of analysis: ten lines worth writing into the order
| Line | Typical band on these esters | What it tells you |
|---|---|---|
| Appearance and odour | Clear colourless to pale yellow liquid | Haze at room temperature signals an acid-fraction problem or water pick-up |
| Colour, APHA or Gardner | APHA 20-150; Gardner 1 maximum on the lightest grades | Oxidation and thermal history; drives colour in white creams |
| Acid value | 0.1-0.5 mg KOH/g maximum | Residual free fatty acid. Read it against SV: free acid share is roughly AV divided by SV |
| Saponification value | 180-350 mg KOH/g depending on acid | Confirms the acid fraction; compare against the calculated value in the table above |
| Hydroxyl value | 5 maximum fully capped; 30-70 on deliberately partial esters | Degree of capping, and therefore polarity and emulsifying tendency |
| Iodine value | 1 maximum on saturated grades | Unsaturation, hence oxidation risk; essential if any of the feedstock was unsaturated |
| Water content, Karl Fischer | 0.1 % maximum | Moisture carried in raises hydrolysis risk and hazes the batch |
| Viscosity, with temperature and method | See the ladder above | The single most under-specified line on emollient ester purchase orders |
| Refractive index at 20 °C | About 1.43-1.46 | Fast identity and purity check; also a rough proxy for the gloss the ester will give |
| Density at 25 °C | 0.89-0.97 g/cm3 | Needed for any volumetric dosing, and useful as a second identity check |
Storage is straightforward but not optional. Keep these esters sealed, away from light and heat; the dipentaerythritol grades can solidify in cold weather and should be warmed gently and mixed before use rather than decanted as a solid. Shelf life of two to three years is typical on a technical grade, and hydrolytic stability - the property the neopentyl core was designed for - means the acid value should barely move over that period. Check it anyway when a drum has been open for a season.
Regulatory position
The Cosmetic Ingredient Review panel assessed 16 pentaerythrityl tetraesters, including pentaerythrityl tetraisononanoate, tetracaprylate/tetracaprate and tetracocoate, and concluded they are safe in the practices of use and concentration reported in that assessment. The Chinese cosmetics safety-assessment database cites a maximum leave-on use level of 7 % for the corresponding tetrastearate, while reported use of the ethylhexanoate and ethylhexanoate/benzoate variants in leave-on products runs considerably higher. Neopentyl Glycol Diheptanoate is listed in the China IECIC inventory, and these esters appear on the EU CosIng inventory and are covered by REACH registration. The wording matters: "safe as used" is tied to the reported practices, so a large jump in use level, or a new application site such as the eye area, needs its own supporting data rather than a citation of the original assessment.
Where to start
If you need one decision rule from this guide, use the calculated saponification value and the hydroxyl value together. The first tells you whether you have been sold a short-acid ester or a long-acid one; the second tells you whether it was fully capped. Neither number distinguishes propylene glycol from neopentyl glycol from pentaerythritol, and that is precisely the point: for texture claims, buy on INCI and viscosity, and use the analytical numbers to police the batch.
Polyol ester emollients available from Shanghai Better Chemical:
- Neopentyl glycol core: Neopentyl Glycol Diheptanoate (CAS 68855-18-5), Neopentyl Glycol Diethylhexanoate (CAS 28510-23-8), Neopentyl Glycol Dicaprylate/Dicaprate (CAS 70693-32-2).
- Trimethylolpropane core: Trimethylolpropane Triethylhexanoate (CAS 26086-33-9), Trimethylolpropane Tricaprylate/Tricaprate (CAS 11138-60-6), Trimethylolpropane Triisostearate (CAS 68541-50-4).
- Pentaerythritol and dipentaerythritol cores: Pentaerythrityl Tetracaprylate/Caprate (CAS 68441-68-9), Pentaerythrityl Tetraisononanoate (CAS 93803-89-5), Pentaerythrityl Tetracocoate (CAS 92201-72-4), Dipentaerythrityl Hexacaprylate/Hexacaprate (CAS 68130-24-5), Dipentaerythrityl Pentaisononanoate (CAS 84418-63-3).
- Propylene glycol core: Propylene Glycol Dicaprylate/Dicaprate (CAS 58748-27-9), Propylene Glycol Diethylhexanoate (CAS 93981-97-6).
Related reading: our guide to branched ester emollients covers the acid-side branching question in more depth, and polyol ester base stocks covers the same chemistry on the lubricant side.
Tell us the polyol core, the acid, the viscosity band at a stated temperature and the application - a sunscreen oil phase, a lipstick, a light lotion - and we will quote the grade, the packing and the documentation that fits.