A humidity indicator card (HIC) 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 has usually been a blotting paper impregnated with cobalt(II) chloride base; Less toxic alternatives include other chemicals such as cobalt-free chloride base and special plastic films.
Humidity indicators are an inexpensive way to indicate or quantify moisture content inside sealed packaging. They are available in many configurations and used in many applications, especially military and semiconductor. The most common humidity indicator cards change color from blue (less than indicated RH level) to pink (greater than indicated RH level).
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