Acid Bond Concentration Professional Sulfate-Free Conditioner for Damaged Hair Redken | Concentrated sulfate-free repair conditioner for damaged hair. This conditioner is the richest formula in Redken To repair damaged hair. Provides complete and intense conditioning and protection against hair discoloration. The acid binding concentrate leave-in is formulated with citric acid, which strengthens the hair fiber, provides shine, and reduces hair breakage. This conditioner balances the pH since it was formulated with a pH acid to protect hair from the negative effects of coloring and external agents.