Why is straight, blonde hair preferable to other types in the construction of a hair hygrometer?
Hygrometers (an instrument used to measure the moisture content or the humidity of air or any gas) that use human hair determine moisture content based on the principle that organic substances (hair) contract and expand in response to the relative humidity. It has been reported that blond hair shrinks more than brunette hair when the air gets moist. I searched and couldn’t find anything related to the straightness of the hair used, but I did find this: The longer the hair, the greater cumulative change in length due to humidity changes. If one inch of hair contracts 0.01 inch with a 30% increase in relative humidity, then a 10 inch strand of hair would change 0.1 inch for the same 30% change in humidity.
