Which perm tool is responsible for determining the size and shape of the new curl texture?

The perm rod is integral to the perming process as it directly influences the size and shape of the new curl texture. When hair is wrapped around the perm rod, the diameter of the rod dictates the final curl. For instance, smaller rods create tighter curls, while larger rods yield looser waves. The way in which the hair is wrapped around the rod also impacts the overall curl pattern and texture; the tension and angle of wrapping can enhance the desired effect.

While other tools such as a comb, brush, or foil play roles in the overall hair styling process, they do not serve the same function in altering the curl's size and shape. The comb is typically used for sectioning or smoothing hair, the brush is utilized for styling or detangling, and foil is primarily used for techniques like highlighting rather than perming. Thus, the perm rod is the crucial component for achieving the specific curl result in a perm treatment.