Isobutylene/Styrene Copolymer

AKA: Butyl Styrene Copolymer

Synthetic

Occlusive

Not Clean

Benzene, ethenyl-, polymer with 2-methyl-1-propene

CAS #

9011-12-5

Form

Liquid

State

Solid

Skin Types

●all-skin-types

Best For

General

Pregnancy & Breastfeeding Safe

Yes

Functions

Film Forming

Creates a physical seal on skin to lock moisture in and keep irritants out. The "slugging" ingredient — barrier protection.

Viscosity Controlling

Polymer With 2 Methyl 1 Propene

The paper trail

🔬Peer-reviewed1 paper →

⚖️Regulatory1 listing →

🛡️Safety-assessed1 review →

Counts, not a verdict. A listing isn't a study. The trail, you decide.

EWG

CIR

Safe as used

Pregnancy

Yes

Restricted By

Concentration Guide

Leave-on1%

Rinse-offNot reported

0%50%100%

CIR reported use · 2014 survey

Regulatory Status

USA✔ permitted

EU⚠ restricted

JAPAN⚠ restricted

CANADA⚠ restricted

Regulatory Agencies

Verified Jun 2026

Data: CosIng · EWG · CIR