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
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
Traditional Use
Synthetic polymer created as a cosmetic ingredient in the 20th century. Formulated to provide film-forming and texture-enhancing properties in skincare, sunscreens, and color cosmetic products.
EWG
4
CIR
Safe as used
Pregnancy
Yes
Restricted By
CIR Safety Findings
medical-approval
all-shades-safe
Regulatory Agencies
Skin Types
●all-skin-types
Best For
General
Pregnancy & Breastfeeding Safe
Yes
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.
Verified Jun 2026
Data: CosIng · EWG · CIR