Pro Longer Mask for long hair helps thicken the appearance of long hair for visibly healthier and stronger looking lengths. The Filler A-100 technology used is patented to L'Oréal Professionnel and works by penetrating the hair fibre 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.​ To use: After Pro Longer shampoo, apply to towel-dried hair. Leave in for 3 to 5 minutes. Rinse thoroughly.