COSRX The Hyaluronic Acid 3 Serum is a lightweight, water-based serum designed to provide the skin with intense hydration. With its three distinct hyaluronic acid molecular weights, it can hydrate the skin to the greatest extent possible by penetrating it at various depths. Additionally, using this serum together with other skincare products can assist to increase the efficacy of those products by plumping up fine wrinkles, leaving skin feeling and appearing smoother and more luminous.