Final answer:
For a body wave perm, large perm rods should be used to create gentle waves instead of tight curls. The rod size must be selected based on the hair's length and texture, and it is best to consult with a hairstylist for the perfect size.
Step-by-step explanation:
To achieve a body wave, which is a type of perm that provides volume and loose waves, you should use larger perm rods that correspond to the desired wave size. Large perm rods are typically used to create gentle waves rather than tight curls. It's important to select a rod size that matches the length of the hair and the type of wave desired. For a body wave, you're aiming for a soft, natural look rather than tight spirals, so choosing a rod that is too small will not yield the intended results.
Remember that the actual size may vary depending on the length and texture of the hair, with long, thick hair possibly requiring a slightly larger rod than shorter hair. As always, it is best to consult with a professional hairstylist to determine the right approach for each individual's hair type and desired outcome.