Final answer:
Volume in thermal curls is achieved by using larger sections of hair, as it creates looser curls that add body to the hairstyle, unlike tighter curls from smaller sections.
Step-by-step explanation:
Volume with thermal curls can be achieved by using larger sections of hair. This is because large sections tend to create looser curls which add body and fullness to the hairstyle. In comparison, using smaller sections of hair would result in tighter curls, which may not necessarily contribute to the overall volume as much. Importantly, it's not about the heat setting or increasing the temperature that creates volume; it's primarily about the size of the sections of hair being curled.