FAQ on Desiccants & Dehumidifiers
Answers to frequently asked questions about moisture protection at ThoMar
Desiccants are small helpers with a big impact: they protect products from moisture, mold, and corrosion – during storage, transport, or in everyday life. But how do they work, how do they differ, and which desiccant is suitable for which application? In our FAQ, we answer the most important questions about the selection, application, and effect of desiccants.
What is a desiccant?
Desiccants or drying agents are hygroscopic granules, meaning they actively attract and store water or moisture from the ambient air. The granules are usually filled into bags made of special materials. The bag material must protect the desiccant from contamination, but at the same time be water vapor permeable to ensure the absorption of humidity. Desiccants can directly influence the climate in an enclosed space, as the absorption of water by the desiccant reduces the absolute and relative humidity of the air.
While the term desiccant is common in industrial applications, the term dehumidifier has become established for home use. You can find out more about dehumidifiers in the FAQ section “Dehumidifiers for Leisure and Car”.
What is the "desiccant method"?
To prevent moisture damage, such as mold, rust, and softened cardboard, during transport and storage, the “desiccant method” is applied. This involves protecting the goods by adding desiccant to a closed enclosure, the so-called “barrier envelope”, or to a closed space. The desiccant absorbs moisture from the air and reduces the relative humidity to safe moisture levels.
What types of desiccants are there?
Desiccants are categorized based on their granulate composition. The different types of granules are all suitable for various purposes.
The most common types of desiccants are:
- Silica gel
Often packaged in the form of transparent beads. Depending on quality, it can store 25-39% of its weight in water. Silica gel, sometimes also written as Silica Gel, is regenerable, but regeneration is rarely worthwhile due to the low cost of the material. Exceptions are specially impregnated silica gels for laboratories or test facilities. - Clay-based desiccants
Clay is the most common desiccant material in Germany for shipping with relatively small volumes. Clay granules can store 30% to 35% of their weight in water. Clay granules such as bentonite are increasingly used, for example, in DIN 55473 desiccant bags. - Salt-based desiccants
Salt-based desiccants can be divided into drip systems made of pure salt and combination systems with swelling agents. Drip systems are used for storage, especially in private households. Since salts liquefy, brine forms in drip systems, which can pose a risk to goods or surfaces if it leaks. Swelling agents have been developed to bind the resulting brine, thus preventing leakage immediately after formation. - Molecular sieves
Molecular sieve is the functional term for synthetic zeolites (or other substances) characterized by high adsorption capacity and rapid uptake rate for certain gases, vapors, or liquids. For this purpose, the pore diameters of the zeolite are adjusted to the size of the molecules to be absorbed (e.g., H2O / water molecules). Molecular sieves are used in many industries and systems.
What are the sources of moisture during transport and storage?
The various moisture sources are visualized in the following illustration:
For correct dimensioning, all four moisture sources must be considered. In this closed system, moisture values can either be precisely calculated using formulas or estimated based on empirical values. Our customer service is always available for consultation.
How does moisture get into the goods?
Air stores significantly more water at high temperatures than at low temperatures. The maximum absorption capacity of 100% is 30.4 g/m³ at 30 °C, but only 6.8 g/m³ at 5 °C. If the temperature drops by 25 °C, but an absolute humidity of 26 g/m³ is present, almost 20 g/m³ will be released. Since moisture cannot escape through the outer shell as temperatures fall, it deposits on and in the goods or packaging materials.
Conversely, as temperatures rise, moisture migrates from the goods or packaging materials into the air. For example, when packing in a warehouse, a damp wooden pallet can increase the originally low relative humidity of, for example, 30% to 80% inside the packaging. Severe temperature fluctuations are not only caused by transporting goods through different climate zones. The difference between a day with strong sunlight and the following night alone can amount to over 50 °C in shipping containers. 
What do the terms "relative humidity" and "absolute humidity" mean?
The absolute humidity of the air is the amount of water present in the air, expressed in grams per cubic meter. Absolute humidity is independent of temperature and provides information about the actual water vapor content of the air.
Relative humidity, on the other hand, is much more important for the transport and storage of goods. Air can only absorb a certain amount of water before it is considered “saturated”. This property depends on the air temperature: warm air can absorb more water vapor than cold air. This is where relative humidity comes into play. It represents the ratio of absolute humidity to the possible saturation amount, in other words, the degree of saturation of the air at a given temperature. The temperature dependence of relative humidity means that as temperatures fall and absolute humidity remains constant, relative humidity rises sharply, because the air’s capacity also decreases with falling temperatures.
This phenomenon is clearly illustrated by the following climate table. The table shows the water vapor content of one cubic meter of air depending on temperature and relative humidity. The upper row shows the water vapor content of the air in g/m³. The lower row describes the dew point temperature in °C. 
What damage can be caused by excessively high relative humidity?
The types of damage vary from goods to goods. Below you will find a selection of damage manifestations.
- Corrosion damage: Ferrous products (machinery, technical instruments, or canned food) tend to rust at higher humidity levels. The corrosion threshold is approximately 40% relative humidity.
- Mold: Cargoes or cargo securing of organic origin, including unprocessed foodstuffs, textiles, leather, or wood and wood products, tend to develop mold. Even non-organic materials such as pottery can be prone to superficial mold growth. The mold growth limit is approximately 75% relative humidity.
- At 100% relative humidity, water vapor condenses into water. Consequences can include: staining and discoloration, collapse and failure of cardboard packaging, detachment of labels, or clumping and swelling of bagged goods.
If you would like to know the exact damage patterns for your goods and how to prevent them, our customer service will be happy to assist you. A short message via the contact form is sufficient.
How much desiccant do I need?
When determining the appropriate amount of desiccant, various factors must be considered. At the following address – Calculate desiccant – we have summarized the most important factors for you. Of course, our team is happy to assist you with any questions and help you choose the best possible desiccant for your application. Simply send us a message via the contact form.
What is cargo sweat?
Cargo sweat refers to the condensation of liquid on the surface of goods. This occurs under the following conditions:
In direct contact between air and goods, the air temperature must cool below the dew point for condensate to form. This occurs when the goods are cooler than the air and have at most dew point temperature. This effect is produced not only during container transport from cold to warm regions or by heating of a shipping container cooled overnight by solar radiation. Even the temperature differences between night and day in Central Europe can be sufficient for condensation to occur in a storage container.
When does one speak of container condensation and container rain?
Container condensation refers to the accumulation of condensate on the inner surface of the container, which usually occurs under the ceiling. The accumulations collect into droplets due to their surface tension, which eventually drip due to their weight. The dripping of water is referred to as container rain.
This effect is caused by direct contact between a cold container wall and the warmer ambient air. When the air is cooled below the dew point temperature by contact with the surface, condensate forms. The temperature discrepancies required for this occur during transport from warm to cold regions. Likewise, the cooling of container walls at sea in the evening can produce this effect. And, as with cargo sweat, this effect can also occur in containers used as storage spaces when, for example, daytime temperatures in spring reach almost 20 degrees, but nighttime temperatures still drop to just above freezing.
Which desiccants are suitable for containers and large spaces?
Shipping with containers presents new requirements for the “desiccant method” described under “Basic Knowledge.” A higher air exchange rate than in-box shipping, extreme climatic conditions, and long travel times require very high-performance desiccants. The clay granulate desiccants according to DIN 55473, formerly known as container desiccants, can only provide this to a limited extent. The amount of desiccant required to achieve a relative humidity of, for example, 40% would be uneconomically high. Additionally, the desiccant saturates after a few days—it may already be saturated before the container leaves the port. After that, your goods remain unprotected.
For the requirements of container transport, whether by sea or rail, and also for storage in containers, salt-based desiccants have been developed. Salts are highly hygroscopic and can absorb immense amounts of water. Two categories can be distinguished:
- Salt-swelling agent mixtures
- Salt drip systems
Clay or starch are typically used as swelling agents, with starch being many times more efficient. Our SeaDry, a high-performance desiccant for use in container transport and storage, consisting of nearly pure calcium chloride and modified starch, can be found here.
Drip systems consist of a salt depot with air access and a drip tray. Due to the high risk potential from the resulting salt liquid, especially from the rolling and pitching movements of the ship, ThoMar OHG does not offer drip systems for container shipping and advises against their use.
What should be considered when purchasing container desiccants?
Pay attention to the quality of the products offered. Tests by independent institutes regarding water absorption capacity or absorption rate are good indicators of product quality. There are suppliers who claim that their desiccant can absorb over 350% moisture. Ask under what conditions (laboratory? Real test?) this result was achieved.
Additionally, the quality of the wrapping material used is important for risk minimization for your goods. A tear-resistant wrapping material should be used to prevent leakage of the desiccant at all times. Another important point, even if the wrapping material does not tear: How well does it contain the absorbed moisture? Especially with suppliers making very high performance claims, you should inquire how liquid the salt-swelling agent mixture becomes after moisture absorption and whether drops can really not pass through the fleece used.
ThoMar OHG recommends: In the end, do not compare the price per product, but the price per gram of water absorbed. The higher the product quality, the less handling effort, additional weight, and risk for your goods.
Here you can find our product: SeaDry container desiccants.
How long can desiccants for containers and large spaces be stored?
Generally, the shelf life of container desiccants depends on the packaging and its closure. ThoMar OHG uses HDPE bags for packaging, which have a high water vapor barrier. The bags are also resealable, so individual products can be removed if needed. With proper storage, SeaDry can be stored for two years from the production date without problems.
How many desiccants do I need when transporting and storing goods in containers?
Using the list at the following URL – Calculate desiccant – you can compile all relevant factors for your specific application. Our customer service is available at any time for all questions and consultation. Simply send us a message via the contact form.
How should desiccants be positioned in the container?
- Desiccants should be distributed evenly in the container.
- Desiccants should always be placed as high as possible. This is due to the fact that warm air carries more water and rises in the container. The highest moisture content is therefore under the container ceiling.
- Check for damage to the container shell, such as rust holes, cracks, and leaking doors. If possible, seal these before container transport. This naturally also applies if you want to store goods in a container or another type of large space without hermetic air sealing.
How long does the desiccant work in containers or large spaces?
The duration of effectiveness generally depends on the absorption rate and capacity of the desiccants used. These are largely defined by the surrounding climate.
Every substance, including a desiccant, always attempts to establish an equilibrium moisture level. The more moisture present in a system, the more substances such as goods, packaging materials, or desiccants absorb.
A low-dosed desiccant will typically absorb water faster and reach its maximum capacity sooner, as the moisture is distributed among fewer materials. Using multiple desiccant bags can regulate the desiccant activity duration. The different climates of the route as well as loading and unloading climates also play a role here.
How should container desiccants be disposed of?
For disposal, the manufacturer’s instructions must be followed. ThoMar OHG’s container desiccant, SeaDry, can be disposed of in standard quantities via ordinary industrial residual waste.
What is a liquid absorber?
A liquid absorber is a special mixture designed to safely and efficiently bind leaking liquids. Especially during transport or storage of products containing liquids, an absorber such as LiquiDry protects against damage caused by leaks. As soon as liquid escapes, the active granules contained in the absorber absorb the liquid and convert it into a gel-like, leak-proof mass. This keeps the surrounding area dry and reliably protects goods and packaging from moisture damage or contamination.
Which liquids can LiquiDry absorb?
The ThoMar Liquids absorber LiquiDry is optimized for use with aqueous liquids and achieves the best absorption performance in this area. These include, for example, water from leaks in transport packaging, cleaning agents from canisters or bottles and similar liquid containers, saline solutions in medical and laboratory-related environments, as well as blood and urine as part of sample shipping or hygiene tests. LiquiDry® can also be used safely with other biological liquids – for example when transporting deceased persons.
How much liquid can a LiquiDry Liquids absorber absorb?
The absorption capacity of a LiquiDry Liquids absorber depends on the size and design. The superabsorbent granules contained react within seconds to leaking liquids and convert them into a gel that does not release any liquid even under pressure. Depending on the liquid, LiquiDry can absorb many times its own weight: with distilled water, absorption performance reaches up to 250 times its own weight, while with a 0.9% saline solution it is around 60 times. For optimal protection, the suitable absorber bag should always be matched to the potential leak volume. Further information on available sizes and variants of LiquiDry is available in the ThoMar online shop.
Can LiquiDry be used multiple times?
No, LiquiDry Liquids absorbers are intended for single use. The water-soluble paper dissolves immediately on contact with liquid, while the granules bind the leaking liquid within seconds and convert it into a gel. After complete absorption, the absorber is used up and cannot be used again.
Can liquid leak out again from the LiquiDry Liquids absorber?
No, LiquiDry reliably encloses absorbed liquids in a stable gel. Unlike a conventional sponge, it does not release any liquid even under pressure. The innovative gel formation thus ensures a permanently secure enclosure of the moisture – even during longer storage or during transport. LiquiDry Liquids absorber therefore ensure a dry, clean packaging environment and provide effective protection against leaks and moisture damage.
What is the difference between dehumidifiers and desiccants?
These terms refer to the same systems and material combinations. In domestic use, the term dehumidifier has become established over the years, while in industrial applications, desiccants are used.
What types of dehumidifiers are available?
Generally, two systems can be distinguished:
- Adsorbing and absorbing systems
- Drip systems
Adsorbing and absorbing systems typically consist of silica gel, clays, or salt mixtures. These bind water physically or chemically.
Physical adsorption (substances/molecules adhere to the surface of another substance and accumulate there) is a reversible process. Such dehumidifiers are therefore regenerable. These include our airdry car dehumidifiers, Safe Dry cabinet and safe dehumidifiers, and Multi Dry universal dehumidifiers.
In chemical absorption, water molecules penetrate into the interior of a solid or liquid and mix with it. This process is not reversible, which is why absorbing dehumidifiers are single-use products. Our airdry Fun windshield dehumidifier is such a product.
Drip systems consist of a salt depot with air access and a drip tray. The salt depot attracts moisture from the air and liquefies. The resulting brine drips into the drip tray. Since such systems pose a risk of brine leakage during movement, ThoMar OHG recommends using drip systems only for stationary applications.
Drip systems are suitable for wardrobes, storage cabinets, safes, caravan storage, basements and storage rooms, or living spaces.
How can I dry or regenerate my airdry car dehumidifier (airdry Classic, Vanilla Fresh, Ice Fresh and Duo)?
The airdry cushions can be dried on a radiator for reuse. Place the cushion with the foil side on the radiator and heat at medium setting. airdry releases its moisture over an extended period, which can take days or weeks depending on saturation and heating.
For the Classic, Vanilla Fresh, and Ice Fresh product variants, drying to a weight of approximately 1.2 kg can be expected. For the airdry Duo product variant, one bag will have a weight of approximately 700 g after regeneration. The original weight (initial weight) cannot be restored through drying! Please do not attempt to dry the bags beyond the specified values. This can lead to material damage and destruction of the bag.
We recommend drying over an extended period on a radiator, as this method is gentler on the material.
Drying in an oven is possible; however, we would like to point out that we cannot provide any guarantee for this type of drying.
For this, one must first distinguish between two different types of ovens:
- If the oven automatically turns off when the oven door is opened slightly, you should open the oven door from time to time during the drying process to allow moisture to escape.
- If the oven allows the door to be opened without turning off, it is best to wedge a wooden spoon or similar object in the gap to allow moisture to escape.
The temperature during the drying process should be between 60°C and 80°C convection. The drying process can take several hours. Additionally, you should wear heat-resistant gloves when removing from the oven to avoid burns.
The airdry Classic, Vanilla Fresh, Ice Fresh, and Duo product variants are not suitable for drying in the microwave.
Using two airdry units alternately is always advisable. One dehumidifies the vehicle, for example, while the other can slowly dry or regenerate.
How can I dry or regenerate my Safe Dry dehumidifier for cabinets and safes?
Safe Dry can be dried on a radiator for reuse. Remove the dehumidifier cushion from the box and place it with the foil side on the radiator. Safe Dry releases the stored moisture over an extended period, which can take days or weeks depending on saturation and heating. Drying to a weight of approximately 330 g can be expected.
We recommend this slow method of drying as it is gentler on the material. Drying Safe Dry in an oven is possible. Please refer to the regeneration instructions for airdry car dehumidifiers (Classic, Vanilla Fresh, Ice Fresh, Duo).
How can I dry or regenerate my Multi Dry universal dehumidifier?
Multi Dry can be dried in an oven (not a microwave!) or on a radiator for reuse. For oven drying, place Multi Dry on a rack at medium height and set the oven temperature to approximately 175°C. Higher temperatures can damage the bag fleece (however, there is no fire hazard). The drying process takes approximately 4-5 hours. If Multi Dry is dried on a radiator, the drying process takes several days.
Caution: Touching the heated bag and especially the metal clip poses a risk of burns. Use pot holders or protective gloves to remove from the oven.
How can I dry or regenerate my airdry Silica Gel car dehumidifier?
- In the oven: The airdry SILICA GEL can be dried in the oven for reuse at max. 100°C (convection). The cushion releases its moisture over a period of 2-3 hours. Open the door several times during drying to allow moisture to escape.
- In the microwave: Dry at max. 600 W for up to 8 min. If necessary, the drying process can be repeated after a 15 min. break. During the break, open the door of the cooking chamber to allow excess moisture (steam) to escape.
Risk of burns: Please use heat-resistant gloves to remove the dehumidifier bags from the oven or microwave.
Risk of overheating: Never exceed drying times and heating power.
Which desiccants are suitable for use in packaging?
As desiccants within packaging, so-called in-box desiccants, silica gel (glass-like beads or fragments of silicon dioxide) or bentonite clay granulate filled in bags are typically used. ThoMar OHG offers the Desi Dry and CertiDry product families for this purpose.
A more detailed description of the different types of desiccants can be found in the “Basic Knowledge” section.
What does "desiccant according to DIN 55473" or "MIL D 3464E" mean?
These are standards that define the properties of certain in-box desiccants. DIN stands for German Industrial Standard, while MIL represents the American equivalent. The technical bag properties are nearly identical.
All desiccants according to DIN 55473 are directly comparable with each other, as the absorption capacity and absorption rate of the desiccant bags are defined by the standards.
A more detailed description of the properties of DIN desiccants can be found on the corresponding category page.
What does the letter after the DIN number mean, such as DIN 55473-B?
The letter after the DIN number refers to the dust permeability of the wrapping material.
“A: low-dust” is defined in DIN 55473 as: “A maximum of 10 mg of dust per desiccant unit may migrate through the wrapping material.”
[DIN 55473:2015-12, 4.3.2 a) paragraph 2]
And as “Version B: dust-proof”: “Regardless of the desiccant units in the bag, a maximum of 1 mg of dust may be measurable after testing.”
[DIN 55473:2015-12, 4.3.2 b) paragraph 2]
What does DU or Unit mean and what is the difference between the two designations?
DU stands for desiccant unit and describes the amount of desiccant granulate that absorbs a specified amount of water within a defined climate in a specified time. This is not a weight specification.
Depending on the quality and origin of the clay granulate, the weights of a DU may differ from each other.
Unit is the equivalent designation in English. Depending on the origin of the desiccant, this designation may also be printed.
Important: This specification always refers to desiccants according to DIN 55473.
How do I know the required amount of desiccants?
When determining the appropriate amount of desiccant, various factors must be considered. At the following address – Calculate desiccant – we have summarized the most important factors for you. Of course, our customer service is happy to assist you with any questions and help you choose the best possible desiccant for your application. Simply send us a message via the contact form.
How do I use desiccants within packaging?
Just like dimensioning, the application of desiccant bags is also regulated in DIN 55474.
According to the “desiccant method” described under “Basic Knowledge,” the packaging must be supplemented with a barrier layer. This is defined by its property of extremely low water vapor permeability. The barrier layer must be tightly sealed and must not have any holes, cracks, or faulty closures.
The desiccant bags are dimensioned according to DIN 55474 and inserted directly before sealing the barrier layer.
After opening the barrier layer, the desiccants must be removed and replaced before resealing.
Can desiccant bags be regenerated?
Industrial desiccants are not intended for regeneration. The costs for the required energy generally far exceed the costs of replacement. An exception is bulk silica gel, which is used in laboratories, for example, and can be regenerated at approximately 130°C.