How does the degree of curl vary among different perm rods?

The degree of curl created by perm rods is directly influenced by the size of the rods themselves. Smaller rods produce tighter curls, while larger rods create looser, more voluminous waves. This is because the diameter of the rod determines how tightly the hair is wound around it during the perming process. When hair is wrapped around a smaller rod, the hair is forced to bend more sharply, resulting in a tighter curl. Conversely, using a larger rod allows for a gentler curve, leading to looser and more relaxed curls.

Other factors like the length of the hair and the temperature of the perm solution do play a role in the overall perming process, but they are not the primary determinants of the curl's tightness. Length can influence how the curl falls and the overall shape, while temperature affects the processing time and effectiveness of the perm solution but does not dictate the curl's tightness in the same direct manner as the rod size.