HUMIDITY INDICATOR CARDS & PAPERS
The actual moisture content of air within a package, expressed as a percentage of it’s saturation moisture content, is termed the Relative Humidity (RH).
The crucial factor in preventing corrosion and mould growth to stored or in transit items is to keep the RH below 40 to 50%.
Carefully calculated, the use of silica gel or molecular sieve sachets can keep the RH below these levels.
This can be confirmed by the use of humidity indicator cards to give a visual reading of the RH level and to provide an indication as to when the desiccant needs changing.
Humidity indicator cards are made of high quality blotting papers, with the spots impregnated with indicator solutions. They are ‘read’ at the point on the card, where the spots are changing from blue to pink.
They will continue to reflect the changing surrounding RH or can be fully reversed, to all blue, by placing them in a sealed container of desiccant (or a similar very low RH environment).
