999. Cooling One's Self on Yom Kippur

Shvisas Asor 3:4

On Yom Kippur, one is not permitted to sit on mud that is so wet that if one places his hand on it and then touches his other hand, the second hand will also become damp from it. One may not fill an earthenware vessel with water and use it to cool himself because the water permeates the walls of the vessel. One may not even do this with a metal container out of the concern that he may come to sprinkle himself with water. One is permitted to cool off by holding fruit against his skin.

Shvisas Asor 3:5

On the day before Yom Kippur, one may soak a handkerchief in water, wring it out and place it under his clothes. He may use this cloth to wipe his face on Yom Kippur without hesitation even though it is very cool.