A two step method to increase the thickness of human hair in which in Step I, a high pH priming lotion is applied to pre-treat the hair to increase its pH, create an anionic charge and therefore loosen and lift the cuticle layers of the hair. In Step II, an acidic thickening composition is applied on top of the Step I composition to deliver polymers and conditioning ingredients to the hair's polypeptide molecule sites. The Step II components have cationic sites that chemically bond to anionic groups in the hair, making them substantive to the hair wherein they deposit under and around the crevices of the cuticles. The low pH of Step II tightly closes the cuticles, sealing the substantive ingredients to the surface of the hair, providing the hair with increased diameter and long lasting thickness.