This is the time when the proteins sink into the cortex and establish linkages within the hair structure. Fragile hair needs just 30 minutes, but 45 minutes will deliver greater straightening and repair for virgin, normal, very curly, resistant and Afro-Caribbean hair types. Check the hair during the sink-in time to ensure hair remains damp. By covering the hair with a cap it retains its hydration levels, which allows the proteins to deliver maximum straightening and repair.