There is no definitive answer to this question as there are a number of factors that can affect hair thickness, including genetics, diet, and health. However, there are some people who are known for having particularly thick hair, such as the Guinness World Record holder for the thickest head of hair. This title is currently held by Tran Van Hay of Vietnam, who has been growing his hair since 1973. His locks measure an impressive 6.8 cm in diameter at the widest point!