Answer:
to provide insulation
Explanation:
The medullary index is the proportion of the diameter of the hair medulla in regard to the diameter of the entire hair: The equation to calculate the medullary index is medulla diameter/hair diameter. In animals, the hair medulla is generally thicker compared to humans (medullary index approximately 0.5 and 0.33, respectively). The thicker the diameter of the hair medulla, the better is the insulation.