Ingredient review
Isobutylene/Isoprene Copolymer
INCI: ISOBUTYLENE/ISOPRENE COPOLYMER
A synthetic rubber that helps products stay put and resist water, but offers no skin benefit.
In plain English
This is a type of synthetic rubber (similar to what's used in tire inner tubes) that's added to cosmetics to create a flexible, water-resistant film on the skin or lashes. It helps mascara stay on without smudging and makes sunscreen last longer when you sweat or swim. It doesn't moisturize or treat the skin—it's purely a functional ingredient for texture and durability.
Review score
Safety, usefulness, and evidence
Potentially useful with some tradeoffs
The evidence base is useful, but some claims depend heavily on the formula.
Risk flags are low for most users, though the finished product can still irritate.
- Source
- synthetic
- Evidence
- moderate
- Irritation
- low
- Clogging risk
- low
Quick decision guide
Useful, but context matters
Isobutylene/Isoprene Copolymer is generally a lower-concern ingredient when the full formula suits your skin.
Plain-English read
Treat this as a practical screening step before you compare products that contain this ingredient.
- Step 1Start with the score, then check the irritation and clogging risk before judging Isobutylene/Isoprene Copolymer.
- Step 2Use the "Best for" and "Use caution if" sections to match the ingredient to your skin, not just to a marketing claim.
- Step 3If a product stings, breaks you out, or worsens irritation, judge the finished formula and stop using it even if the ingredient scores well.
Score terms in plain English
Irritation risk
lowLess likely to sting, burn, or bother most users, though sensitive skin can still react.
Clogging risk
lowLess likely to feel heavy or contribute to clogged pores for most skin types.
Evidence level
moderateThere is useful support, but formula details and claim strength still matter.
What it is
A synthetic copolymer made from isobutylene and isoprene, commonly known as butyl rubber. In cosmetics, it's processed into a fine powder or solution that can be blended into formulas.
How it works
When applied, the copolymer forms a thin, flexible, water-repellent film on the skin or hair. This film locks in other ingredients, prevents smudging, and improves the product's staying power. It also thickens the formula, giving it a richer feel.
Pros
Excellent water resistance
Helps mascara, eyeliner, and sunscreen resist sweat, tears, and water, so you don't have to reapply as often.
Improves product texture
Gives a smooth, creamy feel to formulas and helps them spread evenly without clumping.
Cons and cautions
No skin benefit
This ingredient does not moisturize, soothe, or treat the skin—it's purely functional for product performance.
Environmental persistence
As a synthetic rubber, it is not biodegradable and may contribute to microplastic pollution when washed off.
Best for
- Anyone looking for long-wearing, water-resistant makeup or sunscreen
- People with oily skin who want products that stay put
Use caution if
- Those who prefer fully natural or biodegradable formulas
- Individuals with very sensitive skin that reacts to film-forming ingredients
Usage tips
Safety summary
Considered safe for use in cosmetics at typical concentrations. The Cosmetic Ingredient Review (CIR) panel has reviewed similar polymers and found them safe when formulated to be non-irritating. However, inhalation of loose powder forms should be avoided.
Research notes
Limited peer-reviewed studies specifically on this copolymer in cosmetics. Safety is inferred from broader reviews of synthetic film-formers. The CIR has deemed related polymers safe for topical use.
Common label clues
- Typical concentration
- Usually 1–10% in leave-on formulas
- Regulatory status
- Approved for use in cosmetics in the US (FDA), EU, and many other regions. No concentration restrictions are typically imposed.
- Common uses
- Mascara, Eyeliners, Water-resistant sunscreens, Lip products
- Environmental note
- As a synthetic polymer, it is not biodegradable and may contribute to microplastic pollution. Some manufacturers are exploring bio-based alternatives.
Good to know
- Often listed near the end of ingredient lists because it's used in small amounts.
- Commonly found in 'tubing' mascaras that form tiny tubes around lashes for easy removal with warm water.
Common questions
What is Isobutylene/Isoprene Copolymer in beauty products?
This is a type of synthetic rubber (similar to what's used in tire inner tubes) that's added to cosmetics to create a flexible, water-resistant film on the skin or lashes. It helps mascara stay on without smudging and makes sunscreen last longer when you sweat or swim. It doesn't moisturize or treat the skin—it's purely a functional ingredient for texture and durability.
What does Isobutylene/Isoprene Copolymer do in a beauty product?
When applied, the copolymer forms a thin, flexible, water-repellent film on the skin or hair. This film locks in other ingredients, prevents smudging, and improves the product's staying power. It also thickens the formula, giving it a richer feel.
Is Isobutylene/Isoprene Copolymer safe for most people?
Considered safe for use in cosmetics at typical concentrations. The Cosmetic Ingredient Review (CIR) panel has reviewed similar polymers and found them safe when formulated to be non-irritating. However, inhalation of loose powder forms should be avoided.
Who should be careful with Isobutylene/Isoprene Copolymer?
Those who prefer fully natural or biodegradable formulas Individuals with very sensitive skin that reacts to film-forming ingredients
Research sources
Ingredient reviews are educational and are not medical advice. Patch test new products and ask a licensed clinician about persistent irritation, allergies, pregnancy-specific questions, or diagnosed skin conditions.