What it is
Polyisobutene is a liquid to semi-solid polymer of isobutylene whose properties depend on its molecular weight, ranging from light tackifying liquids to thicker, more substantive grades. In cosmetics it forms a flexible film, adds body and slip, and helps bind pigments and other ingredients together. In sunscreens it contributes to an even, cohesive film and a smooth, cushiony texture.
Safety & warnings
Polyisobutene is an inert, large-molecule hydrocarbon that is generally well tolerated and is not a fragrance allergen. Heavier, more occlusive grades may feel rich, so very acne-prone users may wish to monitor, but the polymer itself is broadly considered low risk.
Origin & sourcing
Synthetic; produced by polymerizing isobutylene, a petroleum-derived monomer.
Questions everyone asks
What is polyisobutene used for in sunscreen?
It acts as a film former and thickener that helps the product spread into an even, cohesive layer and gives a smooth, cushiony feel.
Is polyisobutene the same as a UV filter?
No. It is a texture and film-forming polymer and does not provide UV protection on its own.