Polyisobutene

If you like your lip gloss with that proper lacquered, juicy look, this ingredient is one of the quiet little workhorses making it happen. Polyisobutene is a synthetic polymer made from isobutene, and in cosmetics it acts mostly as a film former, emollient, and gloss booster. In plain English: it helps products feel smooth, look shiny, and stick around instead of disappearing after the first sip of coffee.

You’ll most often find it in lipsticks, lip glosses, lip stains, and other colour cosmetics where slip and shine matter. It gives formulas that plush, cushiony texture that makes them feel more luxurious on the lips, and its tacky nature helps the pigment and shine stay put for longer. It’s especially handy in long-wear products because it creates a thin, flexible film on the skin rather than just sitting there like an oily layer. That means less feathering and a more even finish, which your lipstick will thank you for. Well, if lipsticks could talk.

Polyisobutene also plays nicely with other thickening and stabilising ingredients. One classic example is its use with polyacrylate-13 and polysorbate 20, where the trio helps build texture and keep oil-and-water mixtures well behaved. It is not the kind of ingredient you use for strong skin-care claims, but as a formulation aid it’s very useful. Compared with some natural oils, it has the advantage of being more stable and less prone to oxidation, so it can help a formula keep its feel and performance over time. For most people it is considered well tolerated, since it sits on the surface and doesn’t try to do anything dramatic. Sometimes the best ingredients are the ones quietly doing the boring but important job of making your makeup look better.

A polymer (big molecule from repeated subunits) that's used as a gloss improver for lipsticks and lipglosses. Its stickiness also helps lip products to stay on longer. 

Combined with polyacrylate-13 and polysorbate 20, it forms a very effective tickener-emulsifier trio.