What is desiccant and what does it do?
A desiccant is a dehumidifying agent which attracts moisture from
the atmosphere. It adsorbs and holds particles of water to itself.
The three most common types of desiccants are clay, silica
gel, and molecular sieve.
What are clay desiccants?
Clay desiccants are non-hazardous,
moisture adsorbent substances created by the controlled drying of a calcium
(bentonite) aluminosilicate clay. This naturally occurring montmorillonite
clay has a special affinity for moisture and is chemically inert and non-corrosive. The
layered structure of clay desiccant attracts and adsorbs moisture onto its
surface and between its layers.
Desi Pak® is
the trade name of the packaged clay (bags and packets) sold by Desiccant City. Desi
Pak will protect the contents of a properly sealed container during shipping
and storage (i.e., the contents of a sealed container will be in the same condition
as when they were packaged for shipment or storage).
Clay is the least expensive of all desiccants and highly effective
within normal temperature and relative humidity ranges. It is used in
most industrial applications requiring humidity control. Clay desiccant can adsorb
up to 28% of its weight in water vapor at 77°F (25°C) and 80% relative
humidity. At full moisture vapor capacity, Desi Pak remains dry
and free-flowing. There is no apparent change in size, shape, or texture
of the desiccant.
Clay desiccant works satisfactorily below 120°F (49°C). Above
120°F (49°C), there is a possibility that the clay will give up moisture
rather than pull it in (silica gel or molecular
sieve are suitable for such temperatures). Accordingly, anticipated
storage and transportation conditions should be considered when deciding whether
or not to use clay.
What is silica gel?
Silica gel is silicon dioxide (SiO2),
an amorphous form of silica which is manufactured from sodium silicate and
sulfuric acid. It is a naturally occurring mineral that is purified and
processed into beaded or granular form. Like clay
desiccant, silica gel is also non-corrosive and chemically inert.
Much like a sponge, silica gel's interconnected pores form
a vast surface area that will attract and hold water by adsorption and capillary
condensation, allowing silica gel to adsorb about 40% of its weight in water
vapor at 100% humidity.
As a desiccant, silica gel has an average pore size of 24 angstroms (24A). Silica
gel desiccant will pull in moisture at temperatures up to 220°F (104°C). As
temperatures increase above 100°F (38°C) the rate of moisture pick-up
will slow down, but the silica gel will still work. Silica gel performs
best at room temperatures between 70°F to 90°F (21°C to 32°C)
and at high humidity between 60% to 90% relative humidity.
the trade name of the packaged silica gel (bags, packets, and canisters) sold
by Desiccant City. Sorb-It is designed to control moisture levels within
a properly sealed container during shipment and storage. At 77°F
(25°C) and 80% relative humidity, Sorb-It can adsorb approximately 35% of its weight in
water vapor. However, unlike a sponge, Sorb-It remains dry and free-flowing
at maximum adsorption capacity.
Desiccant City also offers several types of bulk silica
What is indicating silica gel?
Indicating silica gel is a bead or granule that has been washed
with a concentration of cobalt chloride (a heavy metal salt). The cobalt
chloride is a deep blue color when dry and turns from blue to purple to pink
as it becomes saturated with moisture.
Desiccant City also carries orange indicating silica gel. This
type is a bright orange color when dry and turns green as it becomes saturated
The most common form sold by Desiccant City is bulk silica gel, primarily used in air drying applications.
Another use of indicating silica gel is with a
moisture sensitive product that will be inspected regularly, as the indicating
silica gel gives a quick visual indication of how well the product is doing. Due
to the presence of cobalt chloride, indicating silica gel desiccant should never be used
in contact with products for consumption, such as food or pharmaceuticals.
Desi View® is
the trade name of a bagged indicating silica gel mixture sold by Desiccant
Desi View mixture consists of either 90% clay or 90% silica gel; the remaining
10% is always blue indicating silica gel. Desi View bags are only 10%
indicating silica gel for two reasons: 1) a 10% indicating silica gel content
is enough of a color change indicator to be easily viewed through the bag's
polyethylene side; 2) indicating silica gel is more expensive than non-indicating
Indicating silica gel desiccant is also available in special packet
sizes for use in electronics, pharmaceutical, or food packaging.
What is molecular sieve?
Molecular sieve is a synthetically
produced crystalline metal alumosilicate zeolite. Molecular sieve particles
have a uniform pore structure (created during the manufacturing process). This
enables molecular sieve to separate molecules by size. It is also non-hazardous
and derived from naturally occurring materials.
Molecular sieve is the desiccant of choice for the most demanding
and unique applications. The pore structure of molecular sieve desiccant provides
a higher capacity for water adsorption than either silica
gel or clay at very low humidity levels. Molecular
sieve also retains a higher percentage of moisture capacity at elevated temperatures;
in fact, molecular sieve can hold moisture at temperatures well past 450°F
(232°C). Because of its high affinity for moisture, molecular sieve
is able to bring the relative humidity in packages down as low as 10% relative
The most commonly used pore size for drying applications is 4 angstroms (4A). Molecular
sieve desiccant is also available in 3 angstroms (3A), 5 angstroms (5A) and 10 angstroms
(13X) sizes for specific molecule separation, including gases.
Molecular sieve is the most aggressive of the primary desiccants
(in terms of adsorption rate), so additional handling procedures may need to
the brand name of the packaged molecular sieve (bags and packets) sold by Desiccant
City for controlling moisture levels in sealed containers during shipment and
storage. Desiccant City also offers several types of bulk molecular
What is a desiccant "unit"?
In desiccant terminology, a "unit" is the quantity
of desiccant required to meet the U.S. Military's specification (MIL-D-3464E)
for packaged desiccant products. Under this specification, a unit is
the quantity of desiccant which will adsorb 3.00 grams of water vapor at 20%
relative humidity or 6.00 grams of water vapor at 40% relative humidity at
It may also be helpful to think of a unit as equating to approximately
one ounce of material. More specifically, a one unit bag of Desi
Pak® (clay) contains approximately
33 grams per bag, a one unit bag of Sorb-It® (silica
gel) contains 26 grams per bag, and a one unit bag of Tri-Sorb® (molecular
sieve) contains 32 grams per bag.
When do I need to include a humidity indicator card in my package?
You need a humidity
indicator card if you are concerned as to whether or not the desiccant
in your package is still active. Desiccant becomes inactive under the
- if your package is not properly sealed
- if you don't use enough desiccant in your package to draw down the relative
- if the barrier material (i.e., plastic bag) you use to package your product
has a high moisture vapor transmission rate (which means that a significant amount of humid air is entering your package through the barrier material itself).
For more information on humidity indicator cards, please visit
AGM's Humidity Indicator website or view our Humidity
How does desiccant most effectively protect my product or package?
In order to achieve optimal protection, desiccants should be
used within a closed/sealed moisture barrier or a rigid/sealed container. Humidity
Indicator Cards are generally placed inside the container to show the humidity
level and to indicate when the desiccant needs to be replaced.
What size bags, packets, and canisters are available?
Standard sizes for unit bags are as follows: 1/6, 1/3, 1/2,
1, 2, 4, 8, 16, and 80 units. A unit is roughly one ounce of desiccant
Standard sizes for packets are as follows: 1/4,
1/2, 1, 2, 3, 5, and 10 grams.
Standard sizes for canisters are as follows: 1/2, 1, 2, and 3 grams.
Custom sizes are available to fit your packaging needs, though
such sizes typically carry a significant minimum order quantity.
What industries and products use desiccant?
The largest users of desiccants are the industrial, pharmaceutical,
and the electronic components packaging industries. The following list
shows examples of the types of industries and products that use desiccant products:
• Bulk powdered chemicals
• Cholesterol tests
• Circuit boards
• Documents and paper storage
• Electronic components
• Food packaging
• Glucose tests
• Industrial equipment
• Leather products
• Medical equipment
• Metal and machine parts
• Metal powders
• Pet food
• Military instruments and armaments
• Museum storage
• Oceanographic devices
• Optical devices
• Pet foods
• Photographic equipment and film
• Powdered or beaded glass
• Pregnancy tests
• Relays and communication devices
How are desiccants packaged?
Desiccants are generally packaged in bags, packets, or canisters. (Packets
are sometimes referred to as "sachets" or "pouches.")
Desiccants in bags are commonly referred to as industrial desiccants. They
are primarily used by industry because their medium to large size enables them
to adsorb moisture in heavy duty applications. However, these bags are
commonly used in non-industrial applications as well.
Bagged desiccants are available in:
- Tyvek® (heat sealed)
- Kraft paper (heat sealed)
- Lantuck non-woven rayon/polyester blend (string sewn)
The term "bagged" desiccants commonly refers to any
desiccant which is packaged by the unit.
Desiccants in packets or canisters are commonly referred to
as pharmaceutical desiccants. They are primarily used by the pharmaceutical
industry because of their small size. However, other industries, such
as electronics, optics, and food packaging utilize these packets and canisters
Packet desiccants are available in:
- Tyvek (heat sealed)
- GDTII (heat sealed)
Canister desiccants are available in:
For more information on the composition and porosity of desiccant
packaging materials, please refer to Composition
of SCPP Film Stocks.
How much desiccant do I need?
It depends. The amount of desiccant required is usually
dependent on the following factors:
- volume of air space to be desiccated
- nature of the material to be protected
- moisture surrounding the package
- type of desiccant to be used
- length of time for protection
- atmospheric conditions (temperature and relative humidity) when/where the product is sealed and during subsequent shipment and storage
When Desiccant City (AGM Container Controls) receives a call from someone looking
for a desiccant, our Desiccant Specialists will ask a number of questions to
determine responses to the above information so they can calculate which
type and size of desiccant will work best for the particular application.
To determine the number of "units" required to protect medium
to large products/packages/areas, refer to the Desiccant
Requirements Chart Unit Sizes.
To determine the number of "grams" required to protect small
products/packages/areas, refer to the Desiccant
Requirements Chart Gram Sizes.
You may also use our Desiccant Calculator to determine the amount of desiccant for your application.
For further information on how to determine the
amount of desiccant required for your application, please contact one of our
Desiccant Specialists at 1-800-995-5590. You
can also email our sales staff using the Contact