What are humidity indicator strips?
Humidity indicator strips or cards are small strips of paper (approximately 10 cm x 2 cm) that use a color indication method to detect relative humidity. One common version is made of heavy cardstock that incorporates a strip impregnated with cobalt chloride; the impregnated strip is divided into small colored segments. As the humidity increases, the chemically impregnated segments change from a blue color (dry) through lavender, to a pink color (humid). As the humidity level decreases the spots change from a pink color (humid), through lavender, to a blue color (dry). While these indicator strips are not very precise, they are useful for practically and economically monitoring relative humidity in storage containers and exhibit cases. Humidity indicator strips are more precise than the color-change self-indicating silica gel crystals, as those crystals do not react below 30-40% rH, and only indicate when the gel is completely exhausted. An indicator strip reacts at much lower levels (