Most people have experienced the "bad hair day" that is caused by high relative humidity. Scientists used the changes in human hair to detect and indicate relative humidity in early sensors. Horse hair was also used in mechanical devices to indicate humidity.

When material science began producing hook bolt artificial materials such as nylon, researchers soon realized these synthetic materials were more predictable and more accurately calibrated. The evolution of humidity measurement has led to the solid-state humidity sensor that is relatively cheap, extremely accurate and damage resistant.

The temperature at which hook bolt water vapor begins to condense out of a gas at a specified pressure is called the dew point. It is a common weather report term. It is also important in scientific calculations and is used in manufacturing situations or processes. The first dew point instruments used a chilled mirror to determine the temperature of condensation.

These sensors were expensive and difficult to keep calibrated. Electronic technology used in modern dew point sensors can make measurements at temperatures as cold as -40degrees F.The third common humidity measurement is absolute humidity.