The Oriental Believes
The Oriental believes the healthiest state of the body is cool head and warm feet. Once these elements are out of balance (as in a warm head and cool extremities), the body is out of sync for sound sleep, may suffer from a variety of sleep-related problems, such as stiff and achy muscles, and irritabillity
This philosophy is also relative to the studyies in many countries (Swisszerland, Australia & Japan) about heat loss & sleepiness, head cooling on human sleep stages and temperature etc.
For centuries, Japanese were searching for the right pillow material to keep the head cool. Finally, just a few centuries ago, they discovered "buckwheat hulls" or "sova gara" were the perfect material for cooling and neck support.