Hydrogenated polyisobutene and polybutene: where lip gloss shine comes from

Molecular weights from 300 to 1300, viscosity from 30 to 5000 mPa s, use at 5 to 30 percent, and the tack and gloss trade off no natural oil reproduces.

The shine on a commercial lip gloss is not an oil effect. It comes from a synthetic hydrocarbon oligomer, usually hydrogenated polyisobutene or polybutene, laid down as a film thick enough that it does not break up on lip texture. This page covers the grades, what the data sheet numbers actually mean, how much to use before tack takes over, and where the material genuinely beats castor oil.

• INCI: Hydrogenated Polyisobutene
• Mn 300-1300
• 30-5000 mPa s at 25 C
• Vegan, not natural
• Cannot oxidise

What the material actually is

Isobutene, a four carbon gas taken from the refinery C4 stream, is polymerised under acid catalysis into short chains of roughly five to twenty five monomer units. That product is polyisobutene, and it still carries one double bond, left over at the end of each chain where the polymerisation stopped. Hydrogenating that bond gives hydrogenated polyisobutene: a clear, colourless, odourless, tasteless oily liquid with a density around 0.82 to 0.85 g/mL and no measurable solubility in water.

The backbone explains nearly everything the material does. Each repeat unit is a methylene group followed by a carbon carrying two methyl groups. There is no double bond, no ester linkage, and, unusually for a heavily branched hydrocarbon, no tertiary carbon hydrogen for oxygen to abstract. It is about as chemically inert as a cosmetic liquid gets.

It also differs from the other hydrocarbons on a balm shelf in one way that matters commercially. Mineral oil and petrolatum are fractions separated out of crude and defined by a boiling range and a refining route, which is why petrolatum and mineral oil carry grade questions. This is synthesised from a single monomer, so the drum contains what the reaction made. That is why it appears in brands that will not touch mineral oil.

Reading the INCI: three names that are not the same thing

Three closely related names appear on lip product labels and they behave differently. The label will not tell you which one you are looking at unless you know the distinction, and it will never tell you the molecular weight.

The saturated grade is the one to reach for by default. Polybutene keeps its double bond, which is why it can slowly yellow and develop odour in a way hydrogenated polyisobutene cannot, and why it is used in small amounts for cling rather than as the bulk of a formula. If a supplier sells you "polyisobutene" and the data sheet reports an iodine value above about 1, it is not the hydrogenated grade.

A fourth group is worth knowing: hydrogenated styrene, butadiene or isoprene copolymers, sold as gel formers. They thicken a hydrocarbon phase into a clear, springy gel with far less tack per unit of body than polybutene, and are structurants rather than emollients. On how much a label hides, see INCI names explained.

Grades: molecular weight, viscosity and what to buy

Everything a supplier sells under one INCI name sits somewhere on a molecular weight ladder, and that position, not the percentage in your formula, is what your finger will notice first.

These liquids have no melting point because they do not crystallise. They thin as they warm and thicken as they cool, continuously, with no phase change on the way. That makes them easy to work with: they do not need a separate melt step, they will not set a skin on the jug, and they have essentially no effect on the pour window set out in pour temperatures. Very heavy grades are the exception, and only because a cold drum will not pour.

Refractive index, and why it out-glosses castor at the same level

Gloss is specular reflection: light bouncing off a surface in one direction rather than scattering. Two things set it, the refractive index step at the air to film boundary and the smoothness and continuity of that boundary. The first is easy to quantify and turns out to matter less than people assume.

Read the last row before the rest. Keratin has a higher refractive index than any of these liquids, so if index alone made gloss, a dry lip would be the shiniest thing in the room. It is not, because it is rough. And the step from castor oil to a heavy polybutene is worth roughly a tenth more reflectance in relative terms, which nobody detects side by side without an instrument.

The real advantage is geometric, and it comes from four properties at once.

1. It does not absorb. A vegetable oil partly disappears into the upper stratum corneum over the first few minutes, thinning the film and dulling it. A 300 to 1300 g/mol branched hydrocarbon is too large and too non-polar to go anywhere, so the film thickness you applied is the film thickness you still have. Lipid penetration into skin covers which molecules move and which do not.
2. It does not crystallise. Waxes and butters set as microcrystalline solids and every crystal boundary scatters light, which is why a wax-heavy stick reads matte. There is nothing in a gloss polymer to nucleate.
3. It levels. High viscosity plus low surface tension means the liquid bridges the ridges of a lip instead of draining into them, so the reflecting surface is flatter than the lip underneath it.
4. It stays put. No evaporation, no oxidation, no fatty acid to soap up. The gloss at four hours is close to the gloss at four minutes, which is not true of an oil film.

To measure rather than argue, gloss meters read specular gloss to ASTM D523 at 20, 60 or 85 degrees, with cosmetic work casting a film on black card or a synthetic lip substrate. Readings do not transfer between substrates or geometries, so treat published gloss units as a within-study comparison. The optics are set out in lip colour and gloss physics.

How much to use, and where tack takes over

Gloss climbs steeply with the first ten percent and then flattens. Tack climbs slowly and then accelerates. Where the two curves cross depends far more on grade than on level, which is why a single usage number is useless.

Above 30 percent you are formulating a gloss rather than adjusting a balm, and the structure has to be rethought from the wax up. A worked example is in lip gloss balm and a heavier version in overnight lip mask. If the result reads as grabby rather than glossy, the fixes are in sticky, tacky balm.

What it does to the rest of the formula

Adding twenty percent of a non-crystallising liquid to a stick softens it, and the effect is larger than a straight oil swap because the polymer also thickens the liquid phase, raising the yield stress you feel on application while lowering the hardness you feel on the twist-up. Expect to put one to three points of wax back to hold the same firmness, and balm texture science explains why those two are different measurements.

The compensation is that oil bleed drops sharply. A wax network holds liquid by capillary action and a thicker liquid migrates more slowly, so heavy grades are an effective answer to balm sweating.

Pigment is the other trade-off. Wetting a polar particle needs a polar liquid, and a pure hydrocarbon is a poor dispersant for iron oxides. Build the grind phase on castor oil or an ester and let the polymer be the gloss vehicle, or the colour will settle out of a soft product over a few weeks. The pigment side of that choice is in colourants and tints. Pearl effects behave better, because mica needs suspending rather than dispersing and a thick polymer phase suspends well.

One quiet advantage: the material has no taste and no smell. Castor at 15 percent is detectable on the lips as a faint bitterness that fights sweet flavouring, which is a recurring headache when flavouring a lip product. A gloss polymer contributes nothing to the flavour budget.

Oxidative stability and shelf life

The saturated grades have no double bond, no allylic or bis-allylic hydrogen, and no tertiary carbon hydrogen in the backbone. There is no site for the radical chain reaction that turns oils rancid, so peroxide value stays at or near zero and stays there. Nothing about rancidity and oxidation applies to this material, and adding tocopherol on its account is wasted.

Supplier data sheets typically state three to five years, which is a packaging limit rather than a chemical one. The shelf life of a lip product containing 30 percent gloss polymer is set entirely by the other 70 percent: the unsaturated carriers, the flavour, the pigment treatment. Swapping a polyunsaturated oil for a gloss polymer extends life twice over, by removing a substrate and by diluting what remains, which is why gloss formulas outlast balm formulas.

Two side effects follow from the same inertness. It produces no free fatty acids, so it cannot contribute to the soapy off-taste that hydrolysed oils develop. And Malassezia cannot metabolise hydrocarbons, which puts gloss polymers among the few lipids tolerated on Malassezia-prone skin, alongside squalane and mineral oil.

Long wear and non-transfer systems

The common belief that a harder stick transfers less colour is wrong. Transfer resistance is a property of the dried film, not of the bullet. A carnauba-heavy stick is harder to apply, lays down less product and therefore appears to transfer less, but whatever does reach the lip comes off on a cup just as readily.

Genuine non-transfer systems have three parts: a volatile carrier, a film former, and pigment. The carrier, usually isododecane or a C13-14 isoparaffin, evaporates in something like thirty to ninety seconds. The film former, which is either a silicone resin such as trimethylsiloxysilicate or a hydrocarbon polymer from this family, is left behind as a coherent flexible layer that locks the pigment against the lip. Wax plays almost no part. This is why a long-wear liquid lipstick contains little or no wax and why a wax-based stick cannot be made to behave like one.

For a small maker that is an honest dead end rather than a challenge. Volatile isoparaffins have flash points around 40 to 45 C, which changes how a workshop is set up and how the product ships, and they are rarely sold in hobby quantities. The achievable version is a long-wearing stain plus a gloss top coat, the structure behind most workable natural lipstick and tinted balm formulas. The silicone route is compared in silicones in balms.

Vegan status, natural claims and the microplastic question

Vegan is straightforward. The material is petrochemical, there is no animal input anywhere in the route, and it satisfies every vegan standard. That is a genuine advantage over lanolin, the other material used for gloss and cling.

Natural is equally straightforward in the other direction. Under ISO 16128 the natural origin index is zero, and the private organic standards exclude petrochemically derived ingredients outright, so a certified product cannot contain it. The detail is in natural and organic certifications. Whether that distinction tracks anything about performance or safety is a separate argument, and the answer here is that it does not.

The microplastic question is the one that gets answered wrongly most often. Commission Regulation (EU) 2023/2055, which added a restriction on synthetic polymer microparticles to Annex XVII of REACH and applied from 17 October 2023, defines the restricted material as a synthetic polymer that is solid and contained in particles. Polymers that are liquid at 20 C and 1013 hPa fall outside the definition. Hydrogenated polyisobutene, polybutene and polyisobutene at cosmetic grades are liquids, so the restriction does not reach them. What it does reach is solid polymer particles, and the transition periods are long: lip products, nail products and make-up have until 17 October 2035.

Against castor oil, honestly

Castor oil is the natural alternative and it is not a bad one, earning its place through the hydroxyl group on ricinoleic acid, which supplies viscosity, polarity and cling at once, as set out in castor oil.

The verdict: for peak shine in the first minute at 10 percent, the two are close enough that a panel will not reliably separate them. For shine that is still there after a cup of coffee, for anything that has to be tasteless, and for a formula you want to sell with a three year date, the polymer wins clearly. Castor wins on pigment dispersion, on cost, and on any ingredient list that has to read as natural. Most commercial glosses use both, and so should you unless a claim forbids it. Cost the difference per unit before committing, because at 20 percent of a formula it is not a trivial line.

Where it is the wrong choice

Outside lip products it rarely justifies its price. On the body the goal is not shine, and a cheap ester or a light hydrocarbon gives the same slip and spread for less, with the family of options in cosmetic esters. As an occlusive it works, sitting between a light ester and petrolatum on transepidermal water loss measurements, but you would not choose it for that job alone.

It is equally wrong wherever a certification or a natural positioning is doing the selling, and it is a poor primary vehicle for a heavily pigmented product. Most of the people who regret buying it bought one drum of an unspecified grade, found it either too thin to notice or too sticky to sell, and concluded the material does not work.

The decision rule is short. Pick the grade from the feel you want, because no adjustment of level recovers that choice. Pick the level from the gloss you want, knowing it plateaus near 20 percent. Add one to three points of wax back. Keep a polar oil or ester in for pigment and compatibility. And if the label has to say natural, do not start down this road. How the finished list reads to a customer is covered in reading a balm label.

Reviewed and updated 6 September 2026. Spotted an error? Tell us and we will fix and log it.