Which of the following tools is essential for achieving a curl with a perm?

Perm rods are essential tools used in the perming process to create curls. They are designed to hold the hair in a specific shape while the chemical solution works to change the texture and structure of the hair. The size and type of perm rod chosen will determine the size and tightness of the curls produced. During a perm, hair is wrapped around these rods after applying a perm solution, allowing the hair to be set in the desired curl pattern once the solution is neutralized.

In contrast, blow dryers, flat irons, and curling irons are tools primarily used for styling and finishing tasks rather than for the chemical process of perming itself. While they can create curls or waves in different contexts, they do not play a role in the fundamental process of achieving curls through a perm.