Polymethylsilsesquioxane Buono Silicone No known benefits Polymethylsilsesquioxane at a glance Used as a film former and skin conditioning ingredient Is a powder with round-shaped particles Is used in amounts up to 55.2% in cosmetics Deemed safe as used in cosmetics, with no evidence of toxicity or sensitisation Polymethylsilsesquioxane description Polymethylsilsesquioxane is a polymer formed from the condensation and hydrolysis of the silicone methyltrimethoxysilane. In cosmetics, it functions primarily as a film former and skin conditioning ingredient. In its raw form, it is a powder with round particles. In a survey of cosmetic formulations, polymethylsilsesquioxane was found to be used in amounts as high as 55.2%, but most often at concentrations of 4.9% or less. The independent Cosmetic Ingredient Review panel found that polymethylsequioxane is safe as used in cosmetics, with no evidence of toxicity or sensitisation. This silicone polymer is also not known to clog pores.