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Humidity Indicators For Sealed Containers

Humidity indicator cards and plugs provide external monitoring of humidity levels inside containers.

What are humidity indicators?

A humidity indicator is an object, device or mechanism that visually signals the relative humidity level of its given environment.

Types Of Humidity Indicator Products

We carry the following types of humidity indicators:

1. Humidity indicator cards

Humidity Indicator Cards provide external monitoring of humidity levels inside containers and packages.


2. Humidity indicator plugs

Humidity Indicator Plugs are designed for mounting on reusable or long-term storage containers or in any other humidity-controlled enclosure to detect changes in the relative humidity of the space being monitored.

Need a humidity monitoring solution for your next project? Request a quote on one of our humidity indicator products today!

How do humidity indicators measure humidity levels in a sealed container or package?

A humidity monitoring plug is installed on the outside of a sealed container or package. The rear of the plug, which holds a humidity indicator card in its head, remains inside the enclosure and is exposed to the environment within. The indicator on the plug that is located on the outside of the enclosure allows for visible monitoring of humidity without the need to open the container or package.


Benefits Of Using Humidity Indicators

Humidity indicators enable quick, easy visual inspection of the humidity level of an enclosed environment from the outside.

The ability to make determinations about desiccant change-outs or inspecting cargo without opening that environment saves time and avoids causing a mass influx of water vapor and debris into the environment.


Industry Applications

Humidity indicators have applications across a wide range of industries. Some examples include:

  • Monitoring the internal humidity levels in power transformers
  • Monitoring gas streams post desiccation and pre-combustion in energy plants
  • For use in all storage and shipping applications
  • Monitoring humidity levels in munitions crates
  • Monitoring humidity levels of pharmaceuticals in storage and during transport
  • Monitoring humidity levels of machine components during storage and transport

Find a humidity monitoring solution today!

Frequently Asked Questions

1. What is the tightening torque I should use when installing my humidity indicator?

We recommend 30-40 in-lbs for all humidity indicators we offer that are made of metal except for the TA28X series, which utilize an NPT thread form. For the TA28X series, a higher torque might be required. For the TA380 series (made of SAN plastic), we recommend 5-8 in-lbs, or just finger tight.

2. Can I get a custom humidity indicator?

Yes, our Engineering Department has designed hundreds of modified and custom versions for previous customers.

3. I need an indicator that can sense 50 ppm (parts-per million) of moisture. Will your product do that?

No, you need a humidity measuring instrument (such as a hygrometer), not a humidity indicator. That said, we do provide a moisture analysis service, the Hydra20, which is capable of determining the environmental control materials and processes required to maintain a sealed environment at a specific humidity level for any duration.


1. Are humidity indicator cards reusable?

Some humidity indicator cards are reusable, but not all. “Reusable” indicator cards are known as Reversible Humidity Indicators. The name alludes to the nature of some of the chemicals used and their ability to revert to the original color once a humidity level reduces back below the indicator’s humidity threshold.  

2. What is the shelf life for your humidity indicator cards?

The shelf life for humidity indicator cards varies depending on the card. However, most humidity indicator cards have a 3-year shelf life.

3. After the card turns pink, do I need to replace it?

No, once the card turns pink you don’t have to replace it. The card will turn from pink back to blue once it is exposed to an atmosphere that is dryer than the rating on the card.

Important Note: Non-reversible Humidity Cards (Maximum Humidity Indicators) will not return to their original color once exposed to moisture.

4. How long will it take for the card to turn from blue to pink (or pink to blue)?

The time it takes for the card to turn from one color to the other depends on the amount of humidity the card is exposed to and the temperature of exposure. Normally, the cards will change color within minutes of exposure to the ambient conditions.

Important Note: Non-reversible Humidity Cards (Maximum Humidity Indicators) will not return to their original color once exposed to moisture.

5. What is the effect of temperature on the cards? Will they still work?

The humidity rating on the cards changes at the rate of 2-1/2% of the rated value per 10°F away from 75°F. That is, for a card that is rated at 30%, when viewing it at a temperature of 35°, the true value becomes 27%. (2.5 x 4 = 10% rating change, applied to a rating of 30% = 3%, 30% – 3% = 27%.) It works in the opposite direction for higher temperatures.

6. How low of humidity can AGM humidity indicator cards sense?

Standard rectangular cards are available as low as 5% and 8%. Humidity Indicator Plug cards are only as low as 10%. This is because establishing the color of the card in the plug is more difficult than reading a card that is in your hand. The lower 5% and 8% values are difficult to read due to the small amount of chemicals present, which results in a very low-density coloration. Think of a particular color that has had much more white added to it.

7. Are AGM humidity indicator cards reversible?

The reversible ones (which is most of them) are, and the irreversible ones (the Maximum Humidity Indicator cards) are not. This is because Maximum Humidity Indicator cards need to warn of dangerous humidity levels, and therefore serve to indicate the need for desiccant replacement regardless of when they are checked.

8. Are AGM humidity indicator cards supplied with mounting hardware?

Some of them are supplied with mounting hardware. We shift the part number series by one when they are supplied without mounting hardware.

9. How do I replace the humidity indicator card inside the plug and what wrench size is required?

Follow these simple steps to replace your humidity indicator card inside the plug:

  1. Hold housing by the 1.375” hex flange.
  2. Insert a 1/2” hex wrench (Allen wrench) into the lock screw & turn counter-clockwise to loosen.
  3. Remove the lock screw.
  4. Remove the Teflon washer.
  5. Remove the old humidity indicator card.
  6. Install a new humidity indicator card.
  7. Install Teflon washer.
  8. Install the lock screw.
  9. Hold housing by the 1.375” hex flange & torque lock screw to 50+/-5 inch-pounds.


1. Can I mount a humidity indicator plug in my bag?

Yes, you can mount a humidity indicator plug in your bag but you will need the mounting nut version to do this.

2. What pressure can AGM humidity indicator plugs withstand?

All of our humidity indicator plug designs will withstand 10 psig in either direction while our TA284 series is guaranteed to 500 psig outward for high-pressure applications.

Most units are rated to 10 psig in the pressure relief direction. This means the higher pressure is behind the window trying to push the window out of the container. The few vacuum direction tests we have run have shown that the TA356 series at least will also hold 10 psig in the vacuum relief direction.

3. How tight should AGM humidity indicator plugs be tightened?

Both the flange and the mounting nut are 1-3/8” hex shapes. So any suitable hand tool that is capable of engaging a 1-3/8” hex will work. We recommend tightening the mounting nut to 30-40 in-lbs.

We recommend 30-40 in-lbs for all humidity indicators we offer that are made of metal except for the TA28X series, which utilize an NPT thread form. For the TA28X series, a higher torque might be required. For the TA380 series (made of SAN plastic), we recommend 5-8 in-lbs, or just finger tight.


This thread is misleading because it actually has a maximum major diameter of 1.027”. Therefore, the recommended mounting hole diameter is 1.050″ (26.7 mm). This thread is commonly used on the small bung of a 55-gallon drum. The reason our humidity indicators have this thread is that they were initially used most commonly on 55-gallon drums.

Find A Humidity Monitoring Solution For Your Next Project

We carry a variety of humidity indicators to help you monitor humidity levels in different sealed environments.


AGM Container Controls, Inc.
3526 E. Fort Lowell Rd.
Tucson, AZ 85716

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