What is humidity? Humidity is nothing more than

airborne water vapour. Relative humidity is the

percentage of water in the air at any given

temperature (e.g. 50% RH at 20 °C) with respect

to the maximum quantity that the air can hold at

that temperature (100% RH at 20°C). The need to

humidify the air usually occurs in winter months,

when the outside air is cold and humid, for instance

-5°C, 90% RH, and is heated in industrial

environments at 20°C with a relative humidity that

is lowered to 15% RH. As a result, the air can seem "dry".