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Isobutylene/Styrene Copolymer
AKA “Butyl Styrene Copolymer”
Ingredient
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Ingredient Facts
Isobutylene/styrene copolymer
AKA: Butyl Styrene Copolymer
Ingredient · Film Forming · EWG: 4
Synthetic
Occlusive
Not Clean
Benzene, ethenyl-, polymer with 2-methyl-1-propene
CAS #
9011-12-5
Form
Liquid
State
Solid
See origin →
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.
Skin Types
●all-skin-types
Best For
General
Pregnancy & Breastfeeding Safe
Yes
EWG
4
CIR
Safe as used
Pregnancy
Yes
CIR Safety Findings
medical-approval
all-shades-safe
Regulatory Status
USA✔ permitted
EU⚠ restricted
JAPAN⚠ restricted
CANADA⚠ restricted
Verified Jun 2026
Data: CosIng · EWG · CIR