Pro Longer mask for long hair helps thicken long hair for visibly healthier and stronger looking lengths. ​When used with the Pro Longer shampoo and ends-filler treatment for long hair, split ends are reduced visibly by 66%.*​The Filler A-100 technology used is patented to L'Oréal Professionnel, and it works by penetrating the fiber core to plump and thicken the hair from the inside. Amino acids in the formula work to strengthen the hair from the outside. The formula works on thin ends, or areas where help is most needed.​*instrumental test shampoo + lotion + maskAfter Pro Longer shampoo, apply to towel-dried hair. Leave in 3 to 5 minutes. Rinse thoroughly.