When i jump at 70 heat off my ship (in a different biome than i started) my heat stone becomes cold again. Same happens when entering/leaving the caves. It saved me a few times now, but it's far from intentional i think so
- be in summer -equip a heatstone -jump on a boat. -paddle to another biome(perhaps not even neccesary) -jump off boat when about to overheat, or overheating already. Same idea for cave example.