These cards change color from blue to pink to indicate the presence of moisture in the air.
The 30% RH card changes color when the moisture content rises to 30% RH. The 10-60% RH card has 6 spots corresponding to 10, 20, 30, 40, 50, and 60% RH that change color individually when the moisture content reaches the indicated level. Both cards return to blue when placed in a dry environment.
These cards are especially useful in conjunction with the compartment desiccator, the mini-dehumidifier and desiccant bags . They can also be placed in a desiccating chamber to indicate the relative humidity within the chamber.