Graphite and copper additives are used to move heat away from pressure points faster than standard foam. They do not create coldness on their own, but they can reduce localized hot spots under shoulders and hips.
Graphite tends to be more common in premium toppers, while copper is usually presented as a cooling plus antimicrobial angle. If you are evaluating claims, compare with gel infusion performance, phase change material behavior, mattress airflow constraints, and thermoregulation science.
A good example is Saatva Graphite Mattress Topper, which often outperforms basic gel toppers in steady-state heat management. But if the room is humid and still, you may see bigger gains from bedroom airflow improvements and moisture-wicking layers.
For practical buying decisions, cross-check this page against best cooling comforters and best cooling sheets so your topper choice matches the rest of the bed.