If you cut one of these hairs in half, you will see that it has a circular cross-section. Flat hair follicles make curly hair that has an elliptical cross-section. Curled follicles produce irregular kinky hair. Hair shape is also an ethnic characteristic. Caucasian hair hs an elliptical cross section giving it a slight curl while oriental hair has a circular cross section causing straight hair.
Black hair has a flattened elliptical cross-sectional shape.
This cross-sectional asymmetry accounts for the irregular kinky appearance of Black hair. Hispanic hair has a cross-sectional shape somewhere between a circle and a flattened ellipse giving it a wavy appearance. Other factors affecting the shape of hair are the chemical bonds that form within hair proteins. Curl is a factor of disulfide bonds within the keratin molecules. Water is absorbed very rapidly causing the hair shaft to swell.