No, this is only true when you look at the fact that an uncovered head is unable to retain heat unlike a coat covered body. Your head makes up about 10% of your body’s surface area, meaning it loses about 10% of its heat.
This popular myth can be traced back to a military experiment from the 1950’s where participants were exposed to an extremely cold environment wearing an artic survival suit. The researchers did make the distinction that an uncovered head would lose more heat than any covered area of the body. These results were later used in a 1970’s Army Manual that incorrectly stated we lose 40% – 50% of our heat through our heads, thus cementing the myth.
Does this mean you don’t need to wear a hat when it’s cold? Again, the answer is No. We are more sensitive to temperature changes in our head, face and chest. So not only will a hat keep in more heat, we will actually feel more comfortable than being bareheaded in the cold.
So Mom was right, we need to wear a hat when it’s cold outside.