Pro Longer multi-benefit leave in treatment for long hair helps to thicken your long hair whilst making it visibly healthier and stronger looking.When used with the Pro Longer shampoo for long hair, there is a 47% hair breakage reduction and split ends are reduced visibly by 41%*. The Filler A-100 technology 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, after application of Shampoo + leave-on