Cyclopentasiloxane, also known as D5 or Decamethylcyclopentasiloxane, is a cyclic silicone compound. It is a clear, colorless, and low-viscosity liquid in form with a very mild odor. Cyclopentasiloxane is widely used in cosmetics and personal care formulations as a lightweight silicone carrier and skin-conditioning agent. It evaporates quickly and cleanly upon application, leaving no residue, which makes it a preferred ingredient in products where a dry, silky finish is desired. It is commonly found in hair care products such as serums and conditioners, as well as in skin care products including primers, foundations, lotions, and deodorants. Cyclopentasiloxane also functions as a solvent and diluent for other silicone-based ingredients.