What is Relative Humidity?

Relative humidity is a term that indicates the amount of moisture in the air relative to the amount of moisture it has the potential to hold at a given temperature. For example, an RH of 50% means that the air contains 50% of the water vapor that it could potentially hold at a given temperature.

How does RH change in a case or enclosure?

The RH level can change constantly and drastically due to many factors. Some of these factors are:

  • the region of the world where the case or enclosure is located
  • seasonal weather changes
  • local weather changes
  • changes in temperature
  • Proximity to moisture producing and humidity elevating sources, such as a lake or coastal environment. Small portable cases or enclosures can be subjected to other factors causing rapid changes in RH as they are moved from indoors to outdoors and from buildings to automobiles or airplanes, and so on

Relative Humidity Conditions

The rate of corrosion in electronics and electronic components is increased dramatically when exposed to high relative humidity conditions. As the %RH approaches the 90-100% level the equivalent of many months of corrosion (at a lower %RH condition) can occur in a short period of time. Conversely, electricity can cause anomalies and failures in electronics and electronic components under extremely dry conditions. Constantly fluctuating RH takes the worst of “too wet” and “too dry” conditions and multiplies them, adding its own adverse effects.

Ordinary desiccants and dehumidifiers won’t solve these problems

The goal of ordinary desiccants, such as silica gel, is to bring the relative humidity level to 0% or, in effect, a “too dry” condition. This is not a good solution since an extremely dry environment can be as destructive as an extremely wet or damp environment.

Additionally, ordinary desiccants have a very small capacity to absorb moisture (water vapor), even when exposed to very high humidity levels. Therefore, they are fully expended, or saturated, well before accomplishing their task. The result is that ordinary desiccants typically reduce the RH level to some low value temporarily and then expend their small capacity – and stop working! After they are spent the RH bounces back to its original level and begins again to fluctuate. The desiccant then needs to be replaced or regenerated.

The bottom line with silica gel desiccants and other dehumidifiers is that there is no continuous and effective control of relative humidity. Except for the short period of time that the desiccant is lowering the %RH before expending itself, the RH is allowed to fluctuate based on ambient conditions.

Humidifiers won’t solve these problems.

At their best, ordinary humidifiers only work to convert an extremely dry environment to one of varying or fluctuating relative humidity. They work by wetting a sponge (or some other object) in an attempt to create a higher relative humidity environment.

Once the humidifier is placed into the dry environment, it attempts to raise the %RH to its own 100% level. In so doing, it dries out. At the point it dries, the %RH is then allowed to fluctuate, as before, based on ambient conditions.

The bottom line with both desiccants and humidifiers is that the RH is not “controlled.”

The Answer – Humidisorb

Ideally, the %RH would be maintained at a constant (or near constant) long-term %RH at approximately mid-range or mid-scale without the need for intervention from the user. This would eliminate “too wet”, “too dry”, and fluctuating %RH conditions.

That is exactly what Humidisorb accomplishes! When a Humidisorb packet is sized correctly for an enclosure, Humidisorb’s unique formulation works to maintain a near-constant %RH without the need for intervention from the user.


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