Low porosity hair refers to hair that has tightly closed cuticles, which makes it difficult for moisture and nutrients to penetrate and nourish the hair. Hair growth rate is largely determined by genetics and varies from person to person, regardless of hair porosity. On average, hair grows about half an inch (1.25 cm) per month, which translates to about six inches (15 cm) per year. However, factors such as age, diet, hormonal changes, stress, and hair care practices can also affect hair growth.