Cyclopentasiloxane

What-it-does: emollient, solvent, silicone

It's a super commonly used silicone that is water-thin and does not absorb into the skin but evaporates from it (called volatile silicone). Similar to other silicones it gives skin and hair a silky, smooth feel

It's often combined with the heavier dimethicone as the two togeather form a water resistant, breathable protective barrier on the skin without a negative tacky feel.