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 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.