If your hair looks flat or fragile even after a fresh wash, a good leave-in can change the game. Viviscal PRO Thin to Thick Elixir is a lightweight, densifying leave-in designed to make hair look thicker, fuller, and easier to style—without weighing it down. It’s part of Viviscal’s professional line that complements the supplements, shampoo, conditioner, and fibers in the same system.