Indicator cards are ideal for ensuring that your moisture barrier bags and desiccants have successfully carried out their job. Moisture sensitive spots on the cards respond to various levels of humidity with a very noticeable color alteration from blue to pink. The indicator card will indicate the humidity level of whatever you are packaging when the card is checked after the bag is first opened. If your application involves any kind of electronics, then the indicator cards for electronics would most likely be best for you.