How much Desiccant to use

How Much Desiccant Do You Need

What is Desiccant?

Desiccants are agents and compounds, such as silica gel or Montmorillonite clay. Their primary purpose is to facilitate and maintain low humidity environments by absorbing excessive moisture content present in the air.

The most typical areas of applications are storage facilities, transportation, or maintenance facilities of various products and materials. Desiccants also come in handy to keep everything from military munitions to keeping gym shoes dry.

What causes moisture damage

Different possibilities can result in water contamination in a closed package or container, and desiccant has a specific purpose of combating these conditions.

  • Presence of water vapour present in the air within a package
  • Any moisture contained within the material inside a package
  • Moistures on and in the walls of a package
  • The penetration of moisture inside a packaging resulting due to leakage or permeation.

Where to Start?

Determine the conditions to maximize the product’s integrity, including the type and size of the container used and other actual conditions such as relative humidity and temperature. Take readings of the environment, as it will help on the selection for the right type of desiccant.

The conditions surrounding the storage and shipment of the product are important factors to monitor. These include the extremes of relative humidity and temperature to which products might get exposed. The duration of the exposure also plays a part. 

The most practical combination of measures of relative humidity and temperature will be the dew point. Dew point, by definition, is the temperature limit at which the water vapour in the air exceeds its saturation point, squeezing out excess water forming dew or condensation.

The dew point can vary and depends on the quantity of water vapours content present in the air. It is higher with moist air and lowers with dry air. An appropriate desiccant tends to absorb all the water vapour present in the air and reduce the relative humidity to a level where water condensation is not possible.

Packaging requirements to take note

  • The total volume of the container’s air space that needs to be desiccated
  • What type of material needs to be protected
  • Is there any moisture present in the surrounding of the package
  • What type of desiccant will be appropriate to use
  • The duration of time that requires the protection
  • Atmospheric conditions, such as relative humidity and temperature. It is essential to take note of the environment on where and how the product packaging takes place. Additionally, what will be the conditions during shipment and storage?


Follow a general rule of thumb that is 1.2 units of an adequate desiccant will help protect approximately one cubic foot of container space. 1 unit of desiccant would be equivalent to 33 gms of desiccant clay bag.

For example, a container with measurements of 15”x15”x12”. This measurement translates to a total of 1.5625 cubic feet or 2,700 cubic inches. It will require approximately 1.9 units of desiccant that is 1.2 multiplied by 1.5625 to keep the container dry.

However, there is a possibility that not all distributors will carry a 1.9 unit bag of desiccant; therefore, the recommendation is to use a round-up amount, which in this case will be a 2-unit bag.

Using more quantity of desiccant than is required is also encouraged in the event of unforeseen circumstances. 

Five Common Desiccants

Montmorillonite Clay

It is one of the naturally occurring absorbents created by the process of controlled drying of a compound known as magnesium aluminium silicate.

Montmorillonite clay can successfully regenerate for repetitive use at low temperatures without any swelling or substantial deterioration. It is highly effective and inexpensive when used within normal relative humidity ranges and temperatures.

Silica Gel

Silica gel, represented as a chemical formula of (SIO2 * H2O), is one of the most commonly used desiccants. It is an amorphous form of silica achieved from the combination of sulfuric acid and sodium silicate.

It has pores that are interconnected, creating a large surface area that enables it to attract and hold any water or moisture by capillary condensation and absorption. Silica gel is exceptionally effective below 77⁰F or 25⁰ C; however, it starts losing its absorption capabilities as the temperature rises.

Molecular Sieve 

This one is alternatively known as “Synthetic Zeolite” or aluminosilicate. Molecular sieve also contains a network of empty absorption cavities and crystalline pores, which provides it with an internal surface area for absorption of 700 m² to 800 m².

It has a uniform structure, which means molecular sieve is better than clay or silica gel as it will not desorb moisture inside the package.

Calcium Oxide (Cao)

Calcium oxide or Cao is a recalculated or calcinated lime with a moisture absorption capacity of up to 28.5 per cent by weight. One of its unique features is that it can absorb a higher quantity of water vapour at extremely low relative humidity compared to other materials.

Calcium Sulfate (CaSO4)

Calcium Sulfate is also well known by its commercial name that is Drierite. It is one of the inexpensive alternates to desiccants available in suitable packaging. The creation of calcium sulfate occurs by dehydration of gypsum in a controlled process.

It is a general-purpose desiccant mainly used in laboratories. It is chemically non-disintegrating, stable, non-corrosive, and non-toxic, and it does not release the absorbed moisture or water on exposure to higher temperatures.

The lower cost of this desiccant also comes with low absorption capacity. Calcium sulfate can only absorb up to 10 per cent of its weight in moisture or water.

Find out more about desiccant bags on our video here.