Ingredient dictionary

Polyisobutene

Polyisobutene is a synthetic, sticky polymer that helps hold ingredients together and gives formulas a smooth, long-wearing film. It is on the label of 34 products in our library. Checked against our library November 6, 2026.

What Polyisobutene does

Binds pigment particles together in liquid liner
Adds water and smudge resistance
Forms a flexible, lasting film
Adjusts the body and feel of formulas

Polyisobutene is made by linking many small isobutene molecules into one long chain. Isobutene is a simple building block obtained during petroleum refining, so the final ingredient is a synthetic polymer rather than a plant extract. Depending on chain length, it can be a thick liquid or a soft, tacky solid.

Formulators use it as a film former and binder. Once applied, it dries to a flexible, water-resistant layer that holds pigment in place and resists smudging. In eyeliner, that means lines that look crisp for longer. It also adds body and helps control how thick or smooth a formula feels on the skin.

Good for

Helpful for long-wear eye and makeup products that need to resist smudging and water.

Frequently asked questions

Is polyisobutene waterproof?

It helps. Polyisobutene forms a water-resistant film, so eyeliner with it tends to hold up better against water and sweat. No formula is fully waterproof, though. Rubbing, oil, and warm water can still move it, so gentle removal works best.

Is polyisobutene natural?

No. It is a synthetic polymer made in a chemical process from isobutene, a petroleum-derived building block. It is not an extract from plants or minerals. Synthetic does not mean harmful; many well-studied ingredients are made this way.