What's the difference between a repair shampoo and a bond-building shampoo?

Repair shampoos (like L'Oreal Elvive Total Repair 5) use proteins and ceramides to smooth and reinforce the hair surface. Bond-building shampoos such as Olaplex N°4 are marketed to work on internal disulfide bonds damaged by bleaching and heat. Reviewers tend to favor bond-builders for chemically over-processed hair and repair formulas for everyday dryness.