Silica Dimethyl Silylate

Fumed silica that has been surface-treated with a silicone group to make it water-repellent. The result is a very fine powder used to control texture rather than to act on skin. In formulas it stops powders clumping, keeps emulsions from separating, absorbs excess oil, and gives products a soft, blurred finish. It turns up in primers, mattifying products, mineral sunscreens and colour cosmetics — anywhere a smooth, non-shiny surface is the goal.

Texture Enhancer. Silicone. Suspending/Dispersing Agent

The primary particles are only nanometres across and fuse into open, branched aggregates, which is what gives the powder an enormous surface area for its weight. That lets it hold sebum away from the skin's surface, which is what produces the mattifying effect. The silicone surface treatment keeps the particles from taking up water, so they stay dispersed rather than clumping in a wet formula. Optically, a fine layer of these irregular aggregates scatters light rather than reflecting it in one direction, which is why skin looks softer and less shiny — an appearance effect, not a change to t…