Glycols are hygroscopic. If placed in an atmosphere containing water vapor, they will pick up and retain moisture. This property is responsible for the many applications of glycols as humectants and dehydrating agents. In many of these applications, glycol-water solutions are used. The addition of water modifies the properties of glycol.
The relative humectant value of glycols is influenced by humidity and temperature variations. These variations for a range of temperatures and humidities frequently encountered in humectant problems are shown in the table below, which may be used to determine the amount of glycol needed to condition a given quantity of a product requiring a humectant.