Which of the following is NOT an example of thermal design tools?

Thermal design tools are specifically designed to use heat to alter the texture and style of hair. The blow dryer, flat iron, and curling wand all employ heat to create specific hairstyles, making them clear examples of thermal styling tools.

Cylinder rollers, while they can be heated and used to set hair, are generally categorized under traditional hair-setting tools that do not rely on direct heat and thermal principles in the same way as the other options. Instead, they are intended for achieving curls or waves through non-thermal means, such as the use of heat from the scalp or by wrapping hair around them while they are heated. Thus, they do not fit the conventional definition of thermal design tools, as they do not specifically involve the application of direct heat like the blow dryer, flat iron, or curling wand. This is why cylinder rollers represent an exception within the context of the question.