Humidity indicator cards are primarily made of pure white paper, typically using high-quality blotting paper. This type of paper effectively absorbs humidity-sensitive chemicals and allows for reversible color changes with humidity. The indicator dots on the card consist of blotting paper impregnated with a moisture-sensing solution. Depending on whether they contain cobalt, they can be categorized into different types:
Cobalt-containing Humidity Indicator Cards: These use cobalt compounds such as cobalt chloride or cobalt bromide as the moisture-sensing material. They are blue when dry and turn pink after absorbing moisture. However, because cobalt chloride is classified as a Group 2 carcinogen under EU Regulation 2004/73/EC, these products do not comply with RoHS environmental standards and their use is gradually being restricted, especially in products exported to the EU.
Cobalt-free Humidity Indicator Cards: These use environmentally friendly cobalt-free compounds to replace cobalt chloride, achieving various color-changing combinations such as blue to pink, yellow to green, and brown to blue. They comply with EU RoHS directives and REACH regulations and are widely used in fields with high environmental and safety requirements, such as electronic components, semiconductors, and optical instruments.
Common dimensions include 103mm×38mm×0.04mm. It supports customized humidity gradients (e.g., 10%~60%) and complies with industrial standards such as IPC/JEDEC J-STD-033D and MIL-I-8835A.