What it is
Dimethicone copolyol is an older INCI designation for a dimethicone backbone grafted with polyoxyethylene and/or polyoxypropylene (polyether) side chains, which make the otherwise water-repellent silicone partially water-compatible. This dual nature lets it act as a mild surfactant and emulsifier and to impart a soft, non-greasy slip. In sunscreens it can help stabilize emulsions and improve spread and skin feel.
Safety & warnings
Silicone polyethers of this type are generally well tolerated and considered low-irritancy. They are commonly used in leave-on products at modest levels with a low likelihood of clogging pores.
Origin & sourcing
It is a synthetic organosilicon polymer made by attaching polyether chains to a polydimethylsiloxane backbone.
History
The name dimethicone copolyol is a legacy term; modern labeling generally uses more specific PEG/PPG dimethicone nomenclature.
Questions everyone asks
Why is this silicone water-compatible?
Polyether side chains attached to the silicone backbone make it partly water-loving, so it can emulsify and disperse in water-based formulas.
What does it do in a sunscreen?
It works as an emulsifier and conditioning agent, helping stabilize the emulsion and giving a smooth, silky feel.