Humidity Indicator Cards: How to Read Them and When to Use Them

A humidity indicator card (HIC) is a small card printed with circles that change colour as humidity rises. You read it by finding the lowest circle that has changed colour and taking the percentage printed beside it: that figure is the relative humidity inside the sealed space. Use a humidity indicator card whenever you need to prove — on arrival, not only at despatch — that moisture protection held all the way through the journey.

How to Read a Humidity Indicator Card

Each circle on the card has a percentage printed next to it, and that percentage is the relative humidity at which that particular spot turns from its dry colour to its absorbed colour. Reading the card is a comparison, not a measurement:

• Find the highest circle that has fully changed colour. That is your reading. If the 40% spot has changed but the 50% spot has not, the humidity inside the pack is between 40% and 50%.
• Watch the lowest numbers first. The lowest-numbered spot that changes tells you when humidity has started to climb; the highest-numbered spot that stays dry tells you the ceiling you have not yet reached.
• Read the whole card, not one dot. A single changed spot near the top of the scale is a warning; several changed spots mean the protection has already been used up.
• Colour change is reversible. The spots go back to their dry colour when humidity falls again, so the same card can be read, dried and read again.

The Two Common Scales

Our humidity indicator cards are supplied on two scales, and the scale should match the humidity you are trying to hold:

When to Use One

A desiccant absorbs moisture whether or not anyone is watching, and plain white silica gel gives no signal at all. A humidity indicator card turns that silent process into something visible, which is why it is used wherever the consequence of failure is expensive:

• Electronic components and integrated circuits — where hidden moisture causes corrosion, or cracks parts at reflow.
• Optical equipment and sensitive components — lenses, sensors and precision parts that fog, corrode or lose calibration.
• Vacuum packaging and barrier bags — a card sealed inside is the simplest proof the barrier held.
• LCD boards, ICs and mixed electronic assemblies — the standard application set for our indicating cards.

It is also the cheapest way to close an argument. When a buyer claims a shipment arrived damaged by moisture, a card read at the receiving end settles whether the pack was dry on despatch and wet on arrival — evidence that protects both parties.

Pair a Card With the Right Desiccant

A humidity indicator card does not remove moisture — it reports it. It works alongside a desiccant, and the two should be chosen together:

• Indicating silica gel changes its own colour as it saturates, giving a first, coarse warning without opening anything. See our colour-indicating silica gel for the blue-to-pink type.
• A colour card gives a calibrated reading that is independent of the desiccant, so you can see the actual humidity rather than just "some" saturation.
• Food, pharmaceutical and EU-facing packs should use a cobalt-free indicator. Blue indicating gel relies on cobalt chloride; the cobalt-free alternatives avoid it.

Placement and Handling

• Seal the card inside the pack, in plain view when the barrier is opened, so the reading is seen before anything is disturbed.
• Keep it away from direct sunlight and never let it get wet — light and liquid water both corrupt the reading.
• Do not place a card where it can be crushed or folded against the product; a creased card still reads, but a damaged one may not.
• Store spare cards sealed and dry. An exposed card left in a humid room reads that room, not your pack.

For electronics shipments in particular, the card is normally combined with a barrier bag and a desiccant sized to the bag — we cover that practice in our guide to protecting electronics from humidity.

Frequently Asked Questions

What does a humidity indicator card actually measure?

It reports the relative humidity inside the sealed space it sits in. Each printed percentage is the humidity at which that spot changes colour, so the highest spot that has changed is your reading.

Can a humidity indicator card be reused?

Yes. The colour change is reversible, so a card that has taken on moisture returns toward its dry colour when the air around it dries out. In practice cards are usually read once at the end of a journey, but they are not single-use in principle.

Do I need an indicating desiccant as well as a card?

They answer different questions. Indicating gel tells you roughly how spent your desiccant is; a card tells you the actual humidity in the pack. Using both is common on high-value electronics cargo.

Are humidity indicator cards safe next to food and electronics?

The card is a printed indicator that stays outside the product and is not ingested. For food, pharmaceutical and EU-facing packaging, choose the cobalt-free type rather than one that uses a cobalt-based indicator.