Ingredient review
Isobutyl Polysilsesquioxane
INCI: ISOBUTYL POLYSILSESQUIOXANE
A silicone polymer that helps makeup and skincare last longer without feeling heavy or greasy.
In plain English
Isobutyl Polysilsesquioxane is a synthetic silicone ingredient that forms a thin, flexible film on the skin. This film helps other ingredients stay put, improves water resistance, and gives a smooth, silky feel. It is commonly used in long-wear foundations, sunscreens, and eye shadows to prevent smudging and fading. Because it is non-greasy and evaporates quickly, it leaves a comfortable, lightweight finish.
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
Isobutyl Polysilsesquioxane 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 Isobutyl Polysilsesquioxane.
- 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 silicone-based polymer made from silicon and oxygen atoms with isobutyl side groups. It is a type of polysilsesquioxane, which are known for their film-forming and water-repelling properties.
How it works
When applied, the solvent evaporates and the polymer molecules link together to create a thin, breathable film on the skin. This film acts as a barrier that locks in pigments and active ingredients, reduces water loss, and helps the product resist sweat and humidity.
Pros
Long-lasting wear
Creates a flexible film that helps makeup and sunscreen stay put for hours, even in humid conditions.
Lightweight feel
Unlike some heavy oils or waxes, it dries to a silky, non-sticky finish that feels comfortable on the skin.
Cons and cautions
Synthetic ingredient
It is a man-made silicone, which may be a concern for those seeking natural or minimal-ingredient routines.
Removal difficulty
The film can be resistant to water-based cleansers, so you may need an oil-based or micellar cleanser to fully remove it.
Best for
- People who want long-lasting makeup that doesn't smudge
- Those with oily skin who prefer a matte, non-greasy finish
Use caution if
- Anyone with a known sensitivity to silicones (rare)
Usage tips
Safety summary
Isobutyl Polysilsesquioxane is considered safe for cosmetic use at typical concentrations. It has low irritation and comedogenic potential, making it suitable for most skin types. Rare allergic reactions are possible, as with any ingredient.
Research notes
Safety assessments by the Cosmetic Ingredient Review (CIR) panel and other bodies have concluded that polysilsesquioxanes are safe when used as intended. Studies focus on their film-forming and water-repelling properties, with no significant toxicity concerns reported.
Common label clues
- Typical concentration
- 1–10%
- Regulatory status
- Approved for use in cosmetics globally, including by the U.S. FDA and EU CosIng database, with no known restrictions at typical concentrations.
- Common uses
- Foundations, Sunscreens, Long-wear makeup, Eye shadows, Lip products
- Environmental note
- As a silicone polymer, it may not be biodegradable. However, its environmental impact is still being studied, and some manufacturers are exploring more eco-friendly alternatives.
Good to know
- This ingredient is often used in combination with other silicones like Dimethicone to fine-tune texture and feel.
- It is considered non-comedogenic and generally safe for most skin types.
Common questions
What is Isobutyl Polysilsesquioxane in beauty products?
Isobutyl Polysilsesquioxane is a synthetic silicone ingredient that forms a thin, flexible film on the skin. This film helps other ingredients stay put, improves water resistance, and gives a smooth, silky feel. It is commonly used in long-wear foundations, sunscreens, and eye shadows to prevent smudging and fading. Because it is non-greasy and evaporates quickly, it leaves a comfortable, lightweight finish.
What does Isobutyl Polysilsesquioxane do in a beauty product?
When applied, the solvent evaporates and the polymer molecules link together to create a thin, breathable film on the skin. This film acts as a barrier that locks in pigments and active ingredients, reduces water loss, and helps the product resist sweat and humidity.
Is Isobutyl Polysilsesquioxane safe for most people?
Isobutyl Polysilsesquioxane is considered safe for cosmetic use at typical concentrations. It has low irritation and comedogenic potential, making it suitable for most skin types. Rare allergic reactions are possible, as with any ingredient.
Who should be careful with Isobutyl Polysilsesquioxane?
Anyone with a known sensitivity to silicones (rare)
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.