The item that needs to be protected is placed inside of an air-tight container or something that can be tightly closed to prevent moisture from getting in, the desiccants is then placed inside the container with the item. It will rapidly desiccate the air inside the container and protect the items from being damaged by any moisture in the air inside.

There are several different types of desiccants which can be used. Depending on what kind of item needs to be preserved and how it is placed in the container.

DriCan
This type is a small canister which is perforated and contains 40 grams of silica gel. It is light weight and can be used for many years since it can be regenerated by placing it in any conventional oven and dried. The canister will change color from blue to pink when it has absorbed as much moisture as it can. Works in plastic pouches, display cases, tool boxes and many other types of containers which can be sealed. It measures 55 by 102 by 13.5 mm (2.16 inches by 4.0 inches by .53 inches.)

Capsule Dehydrators
The capsule type of desiccants use less space, is sift-proof, has controlled absorption, color indicator. Its small size saves on space and weight. Besides helping to reduce humidity, the can protect against such things as odor formation, mildew, condensation and several other problems caused by moisture in a sealed container. Type 11 weighs 0.97 grams and is 8mm by 22mm. Type 14 weighs 1.85 grams and is 8mm by 40mm. Both are available in packages of 100.

Reusable sorbent box
This type is a perforated box containing silica gel. The sides of the box are sealed so that the gel will not spill. It will change colors from blue to pink when it has absorbed as much moisture as it can. To regenerate it, place in a micro wave for 15 to 20 seconds or in a conventional oven at 240 degrees for 3 hours. The color will change back to blue and be ready to use again. The box is 55mm by 55mm by 25mm and weighs 67 grams.

Read more: Types of Dessicants

Montmorillonite Clay is a naturally-occurring form of magnesium aluminum silicate that is capable of adsorbing large amounts of moisture, and can be used repeatedly without deterioration. It is usually the cheapest desiccant type available.

Clay only performs well at temperatures below 50 C. At higher temperatures, it tends to give up moisture instead of adsorbing it. In applications where the desiccant must be used or stored at high temperatures, it is necessary to use some other desiccant.

Silica gel is the only desiccant type that is approved by the FDA for use with products to be consumed internally, so it is generally used in packaging for food and pharmaceutical products. It will perform well up to about 105 C. As temperature rises, the adsorption rate slows but remains high enough to be effective. The ideal environment for silica gel performance is about 70 to 90 degrees F and about 60% to 90% humidity.

Both silica gel and clay have variable pore sizes, and can be used to adsorb substances other than water.

Molecular sieves are more precise desiccant types. These are crystalline substances that can be manufactured with pores of a specific size, allowing them to adsorb certain substances while allowing others to pass. They perform well at temperatures above 230 C, and have a very high affinity for moisture. They have not yet been approved for use with consumable items in the US, but are being used with pharmaceutical products in Europe.

Calcium oxide, also called quicklime, is a form of lime that can adsorb very large amounts of water. It is used in situations where there is a large amount of moisture present, and low humidity is desired. Its disadvantage is that it works slowly, sometimes taking days to remove all of the moisture. It also swells as it adsorbs, making it undesirable for some applications.

Calcium sulfate is a product made from gypsum that is mainly used in laboratories. It is inexpensive and does not lose its moisture at high temperatures. It has a relatively low adsorption rate, adsorbing only about 10% of its weight in water. It is available, but is not normally sold in package form.

Read more: Desiccants and the environment

Some reusable desiccants are used to remove excess humidity. The primary function of doing so is to preserve products that are sensitive to moisture in the air that may otherwise become damaged. Insulated windows are also desiccants. When this type of window is put into the space that is between the edge of the window and the air space, the accumulation of moisture and condensation between the window panes is prevented.

Salt is also a desiccant. It is used to preserve foods by drying them and is also used in mummification. Rice is also a desiccant but is not as effective as salt. Rice is sometimes used in salt-shakers to make shaking and pouring more effective. It is only an effective reusable desiccant if it is surrounded by an environment that is organism-hostile; it is mainly considered an optional alternative.

Other than for drying purposes, they can also be used for fungicidal, virucidal, antibiotic, and pesticidal effects. An example of it being used for antifungal and antibiotic effects is table salt. Salt has natural anti fungal and antibiotic properties and it is also not harmful to consume as long as is not consumed in large quantities. Since it is safe, it used and is suitable for preserving foods.

Other reusable desiccants commonly used include montmorillonite clay, bentonite clay, calcium sulfate, calcium hydride, calcium chloride, molecular sieve, silica gel, activated alumina, magnesium, magnesium perchlorate, magnesium sulfate, benzophenone, aerogel, potassium, potassium carbonate, a sodium-potassium alloy, sulfuric acid, sucrose, phosphorus pentoxide, copper sulfate, cobalt chloride, sodium chloride, sodium chlorate, sodium sulfate, sodium hydroxide, sodium-benzophenone, lithium hydride, lithium chloride, and lithium bromide. Desiccants are better at preserving things if they are chemically inert and stable. Ones that are chalk-based, clay-based, or of the silica gel variety are examples of types that are chemically stable.

Reusable desiccants are commonly used to absorb water. They are measured to be efficient based on the ratio of how much water they can store relative to mass. Performance of desiccants varies due to the temperature of humidity.

Desiccants provide excellent corrosion protection for dehydration applications such as natural gas storage, air dehydration, gas pipeline heaters, etc. Some common desiccants are activated carbon, sodium perchlorate, calcium sulfate, silica gel, salt, and rice. Salt is used to preserve dead bodies especially in hospitals for exhibition and also in Egypt to preserve mummies, which prevents the decay. Rice is used to maintain granularity of salt and prevent the moisture from sticking to the edges of the salt shakers.

They also serve as evaporation means say for example, many objects are allowed to evaporate and if their moisture content matches with the enviornment conditions then it is difficult to allow them to evaporate water on their own, hence desiccants can take care of this job effectively without affecting the environment. They can be used for variety of applications since some desiccants are anti fungal, anti microbial, or anti viral.
Moist metal surfaces are very much prone to corrosion. Desiccants absorb all the moisture on the metals and prevent them from corrosion and hence are very much environment friendly.

Desiccants like salt are not toxic and hence are environmental friendly. Highly reactive desiccants are rarely preferred, people always use chemically stable ones such that they don’t react to any of the existing environment setups causing harmful effects to life. Some desiccants are said to eliminate carbon from air and cool the atmosphere, thus acting as natural coolers during hot summer and saving power.

While packing substances like food grains, it is very much essential that entire air and moisture is removed from the packet in order to prevent the grains from rottening. Hence desiccants can act as absorbents and remove the air and moisture thus reducing the decay. This will very much help in overseas shipping of items such as cameras, books, coin collection, antiques, guns, any other electronic equipments etc. Activated charcoal is the best desiccant for this purpose since it absorbs the moisture and air thus preventing the goods from damage.