Final answer:
Perm hair longer than six inches can be styled using any type of perm rods; the choice is based on the desired perm technique and outcome, not the hair length.
Step-by-step explanation:
To perm hair longer than six inches, you should use perm rods of any type. The term 'perm' refers to a permanent hairstyle, which can be created using either hot perm rods or cold perm rods, depending on the technique and desired outcome. While hot perms typically use thermal methods to create curls with the assistance of heat, cold perms rely on chemicals to set the curls around the rods. Regardless of hair length, the type of perm rod used is determined by the kind of perm the individual desires and the techniques utilized by the stylist.