This is always worth a discussion as there is widespread misconception regarding heat loss through one’s head. CNN published a set of 10 health myths including this one on heat loss through one’s head.
The truth is: “This adage was probably based on an infant’s head size, which is a much greater percentage of the total body than an adult head,” says Pollack. That’s why it’s important to make sure an infant’s head remains covered in cold weather. (This also explains those ubiquitous newborn caps at the hospital.) But for an adult, the figure is more like 10 percent. And keep in mind that heat escapes from any exposed area (feet, arms, hands), so putting on a hat is no more important than slipping on gloves.