Humidity indicator cards are specifically impregnated with a powerful solution of cobalt chloride that has been properly mixed to alter color from blue through several shades of pink and magenta. These kinds of cards are not mere precision indicators. Instead, they have the ability to tell you about the maximum amount of humidity that could be present inside a container. Their absorbing capacity too is very good and they can easily control the humidity level. Companies manufacturing and transporting products like computers, SLR cameras and video cameras use these cards to keep a check on the level of humidity so that the products remain safe during transit.