Desiccant Selection


Proper selection of the right desiccant can be inexpensive insurance for protecting your packaged product. Product quality can be improved, resulting in reduced or eliminated customer rejections.

When dealing with moisture problems in packaging, a wide array of variables can make it difficult or confusing to develop solutions. These variables can be classified into two main groups:
1) those pertaining to the product, its package, and the environment;
2) the physical and chemical properties of commercially available desiccants.

Formal testing can become quite costly in time and money, and the purpose of this entry is to provide basic information about currently available desiccants and their properties. We hope it will help you to make better informed selections.

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What Size Desiccant Do I Need?

It depends. The answer to the size of desiccant needed depends on the size of the air space to be desiccated, the nature of the material in the package, the moisture barrier surrounding the package, the type of desiccant being used, the desired shelf life, the atmosphere conditions where the package is sealed, the type of seal on the package, etc.

Dri-Box has an approximate effective desiccating area of three feet of sealed cubic space, an area our Moisture Control System barrier bags are careful not to exceed. In the case of other desiccants, you should contact us.

We will usually ask a new customer a number of questions to determine the above variables, so that we can calculate which size desiccant will work best in a particular application.

How Does The Environment Factor In?

Temperature, relative humidity and other considerations constitute the product's environment, which must be controlled to match the conditions of optimum product preservation and performance. Before selecting the correct desiccant, professional packaging engineers review the conditions surrounding the shipment and storage of the product: the extremes of temperature and relative humidity to which the product will be exposed and the average duration of such exposures.

The most useful combined measure of temperature and relative humidity is the dew point. Dew point is the temperature at which the water vapor content of the air exceeds saturation and the excess water is squeezed out, forming dew or condensation. The dew point varies with the amount of water vapor in the air. It is low with dry air, and high with saturated air.

For example, at zero°C, the air can hold no more than 4.84 gm/m3 of water vapor; at 40°C the air can hold no more than 50.7g/m3 of water vapor (see the related chart for more details.)

An effective desiccant will adsorb the water vapor in the air, lowering the relative humidity to the point where water cannot condense.

Is Packaging An Issue?

The container in which the product will be packaged, shipped and stored is vital in determining how much of a particular desiccant is needed and in what packaging form. Before the adsorbent selection process itself, a packaging engineer determines the size of the container based on the flexibility of the container's wall structure.

An important factor in the efficiency of the selected desiccant is the bag material (cover stock) of the desiccant. The cover stock must allow the desiccant to do its job without harming the product. This means maintaining an acceptable adsorption rate and conforming to the product's dusting requirements.

The selected desiccant's adsorption rate is greatly affected by the water vapor transmission rate of its cover stock. This is the measure of the gain or loss of water vapor through the package of the bagged desiccant. By their nature, certain products require a very non-dusting desiccant bag to maintain their integrity. While dealing with dusting requirements, however, the packaging engineer encounters another problem: in preventing the release of dust into the container, the water vapor transmission rate is often adversely affected.

The search for a solution has led to the development of substances such as a spunbonded, high-density polyethylene material known commercially as Tyvek®. Created by DuPont, Tyvek resembles a waxy paper with good whiteness and exceptional strength, maintaining its size and shape with changes in humidity. It will not allow dust to be released into the container, is resistant to staining, mold and mildew growth, and will not reduce the adsorption rate of the desiccant it holds.

Because of its special properties, Tyvek is more expensive than conventional desiccant package materials. The Moisture Control System's barrier bags are composed of polyethylene bonded to a specialized grade of aluminum foil for extra strength. See our specific page on the system for more detailed information.