Acid Bond Concentration Professional sulfate-free conditioner for damaged hair from Redken | Sulfate-free concentrated repair conditioner for damaged hair. This conditioner is the richest formula Redken to repair damaged hair. Provides complete, intense conditioning and protection against hair discoloration. Acid Bond Concentrate Leave-in has been formulated with citric acid which strengthens the hair fiber, provides shine and reduces hair breakage. This conditioner balances the pH since it has been formulated with an acidic pH to protect the hair from the negative effects of coloring and external agents.