What it is
Polypropylsilsesquioxane is a cross-linked silicone (silsesquioxane) resin built on a silicon-oxygen network bearing propyl groups. In sunscreens and color cosmetics it acts as a film former, helping the product dry down to an even, flexible layer that resists transfer and improves the durability of the cosmetic film. It also contributes a smooth, non-tacky feel and can help hold pigments and other ingredients in place.
Safety & warnings
Silsesquioxane resins of this type are large, inert polymers that stay on the skin surface and are generally well tolerated, with low expected potential for irritation or sensitization. It is not a known fragrance allergen and is not an oil, so it is not associated with comedogenicity in the way fatty oils can be.
Origin & sourcing
Synthetic; it is a silicone polymer manufactured from siloxane chemistry rather than derived from a natural source.
Questions everyone asks
What does polypropylsilsesquioxane do in a sunscreen?
It works mainly as a film former, helping the product set into a smooth, even, long-wearing layer on the skin while improving the texture of the finish.
Is polypropylsilsesquioxane a silicone?
Yes. It is a cross-linked silicone resin in the silsesquioxane family, used for its film-forming and skin-feel properties rather than for any biological activity.