Nº.0 Intensive Bond Building Treatment primes hair to absorb nourishment for maximum repair. A professional-inspired treatment that primes hair for deeper repair with the highest dose of patented Olaplex technology in any take-home product. It rebuilds hair bonds, strengthens and protects hair integrity. Use as the first step in a two-part system with N°3 Hair Perfecter. Scientifically Proven 68% more repair & 3x stronger hair when used as a two-part system in just one use! Tip: N°0 bottle should last 3-6 applications, based on hair length and density.