Re: How can a hat keep you warm in winter, yet cool in summer?

April,

It's all a question of relative temperatures because heat always moves 
from hot things to cooler ones. So you're quite right that the hat keeps 
your body heat from flowing out to the air when the air is cold, by 
providing a layer of insulation. In hot weather, the sun shining on your 
head will make the skin and hair of your head hotter than your body 
temperature, even if the general air temperature isn't above 98.6F. 
(Remember that the temperatures the weather forecasters give are the shade 
temperatures, not the temperatures of things exposed to sunlight). A hat 
stops the heat radiation reaching your head so you will be cooler.