What is it: This Advanced Hair Thickening Serum is proven to instantly boost hair diameter and protects hair against breakage, allowing it to grow longer* . Why you'll love it: Our advanced formula is specifically designed to boost hair thickness and density, giving you thicker, fuller-looking hair. instantly.** This powerful hair thickening serum not only enhances the thickness of your hair but also strengthens and nourishes it from within, leaving it more manageable. Featured ingredients: Formulated with powerful ingredients like caffeine, wild mint oil, peppermint oil, and niacinamide.