A humidity indicator card (嗝) is a card on which a moisture-sensitive chemical is impregnated such that it will change color when the indicated relative humidity is exceeded.
This item is an inexpensive way to quantify relative humidity levels inside sealed packaging. They are available in many configurations and used in many applications. The most common humidity indicator cards change color from blue (less than indicated RH level) to pink (greater than indicated RH level).
1)The HIC with cobalt(ii) chloride base:
change color from blue to pink.
2)The HIC without cobalt(ii) chloride base:
Environment friendly,change color from brown to blue,some change color from yellow to blue or from blue to red.