Advanced Treatment Thickening Formula. Leaves hair visibly thicker. Prell Thickening Formula is fortified with an exclusive blend of protein and vitamins that nourish individual hairs from root to end, helping them look thicker and fuller. Plus, Prell Thickening Formula is alcohol-free, so it cleans your hair without causing dryness. As this nondrying formula gently cleans, it also infuses your hair with antioxidants and protectants. The result is hair that looks stronger, thicker and healthier. Use Press Thickening Formula everyday and you'll see the difference.