Looking at the inside of the pillow and the filling, cooling gel inserts are very popular as these work to regulate your body temperature and provide a constant cooling sensation.
Pillows filled with hollowfibre are lightweight and made with breathable open fibres that are often hypoallergenic. The open cell structure allows air to be better circulated and hot air to disperse out of the pillow.
Memory foam pillows tend to absorb heat and should be avoided, although some pillows have tiny “air holes” in the memory foam which does help with airflow. Mesh side walls are another popular innovation, again to help expel hot air.