Which of the following is NOT a characteristic of the solid form?

The characteristic that stands out as NOT being associated with the solid form is interior activation. In the context of hairstyling, the solid form is recognized for its clean lines and uniform shape, which is typically achieved through techniques that emphasize the weight and volume of the hair evenly throughout.

Exterior activation refers to how the outer layers of hair are styled or cut to enhance texture and movement. Consistent length is a defining feature of the solid form, as this style typically maintains an even length throughout for a unified appearance. Weight distribution is also integral, as it plays a crucial role in how the overall style sits and moves.

Interior activation, however, involves layering and texturizing techniques that disrupt that uniformity, which is characteristic of other forms and styles but not the solid form. Therefore, this aspect does not belong in the discussion of the solid form, making it the correct choice.