Moisture is one of the biggest threats to products during storage and transit, leading to corrosion, mold growth, reduced product performance, and costly damage. The right desiccant packs help control humidity inside sealed packaging, protecting everything from electronics and pharmaceuticals to industrial equipment and military components. However, choosing the best option involves more than simply adding a packet to a box.
Understanding the differences between silica gel, clay, and molecular sieve desiccants, along with selecting the proper unit size, is essential for effective moisture control.
This guide explains the most common types of desiccant packs, how MIL-D-3464 sizing works, and the key factors to consider when selecting the right solution for your packaging application.
What Are Desiccant Packs?
Desiccants are a type of material used to absorb moisture, humidity, and other contaminants. Desiccant packs work through a process called adsorption, in which moisture molecules adhere to the surface of the desiccant material rather than being chemically absorbed into it. These materials are particularly useful for protecting goods during shipping and storage, as they help to maintain the quality and integrity of the product.
Desiccants come in many different forms, including silica gel packets, clay desiccant bags, and molecular sieve sachets. These absorbent components are contained within a pack made from porous materials such as Tyvek or kraft paper, which allow them to draw moisture from the air within a container. In addition to absorbing water, some desiccants are also capable of absorbing aromatic substances, making them an excellent choice for odor management. There are a wide range of available desiccant pack sizes, starting at 1/6 unit and going all the way up to 80 units (5 1/2 grams to 2,640 grams). To learn how to calculate the right amount for your packaging, see the unit sizing guidance below.
One of the main benefits of using desiccant packs is that they can help to protect products from corrosion. For example, electronic components can be easily damaged by moisture and humidity, which can cause rust, corrosion, and deterioration. Desiccants help to prevent this type of damage by absorbing moisture and humidity, creating a dry environment that is less likely to cause damage to the product.
Another benefit of using desiccants in packaging is that they help to prevent the growth of mold and bacteria. Moisture and humidity can create an ideal environment for mold and bacteria to thrive, which can damage or spoil the product. By absorbing excess moisture, desiccants can help to prevent the growth of these harmful organisms, ensuring that the product remains fresh and safe for consumption.
Types of Desiccant Packs
Choosing the right desiccant pack starts with understanding how the three most common materials differ in capacity, performance, and ideal application.
- Silica gel packs: A versatile, widely used desiccant with strong moisture capacity across a broad humidity range. Silica gel is a popular choice for protecting electronics, pharmaceuticals, and general shipments.
- Clay desiccant packs: A cost-effective option made from naturally occurring montmorillonite clay. Clay desiccant packs are well suited to bulk industrial shipments and larger containers where price per unit matters.
- Molecular sieve sachets: Engineered to maintain strong adsorption performance even at low humidity and low temperatures, making molecular sieve desiccant the preferred choice for military and aerospace packaging that must meet MIL-D-3464 specifications.
The table below compares the three desiccant types side by side.
|
Type |
Moisture Capacity |
Best Temperature Range |
Best Use Case |
|
Silica gel |
Up to roughly 40% of its own weight in moisture |
Effective across a wide range, including high humidity |
Electronics, pharmaceuticals, general shipping and storage |
|
Clay desiccant |
Lower capacity than silica gel, but cost-effective |
Performs well in moderate humidity and standard ambient conditions |
Large containers, bulk industrial shipments, lower-cost applications |
|
Molecular sieve |
High capacity, even at low humidity levels |
Maintains performance at low temperatures and low humidity |
Military, aerospace, and other applications requiring MIL-D-3464 compliance |
Desiccant Pack Sizing: Understanding Units (MIL-D-3464)
Desiccant packs are sized in units, a standard of measure defined by the military specification MIL-D-3464. One unit of desiccant is capable of adsorbing a set amount of moisture under controlled humidity conditions, which allows packaging engineers to calculate the precise amount of desiccant needed for a given enclosed volume rather than guessing.
Royco Packaging stocks desiccant packs ranging from 1/6 unit (about 5 1/2 grams) up to 80 units (about 2,640 grams), covering everything from small electronics enclosures to large equipment crates. As a general rule, the larger the enclosed air space and the higher the expected humidity exposure during transit or storage, the more units of desiccant are required. A Royco Packaging product specialist can run these calculations for your specific container dimensions, expected humidity, and shipment duration.
Need desiccant packs that meet MIL-D-3464? Royco stocks silica gel and clay packs ready to ship.
Applications by Industry
Desiccants are commonly used in a variety of industries, including food, pharmaceuticals, electronics, textiles, aerospace, and industrial. In the food industry, desiccants are often used to protect dry goods, such as grains, nuts, and seeds, from moisture and humidity, and ESD-sensitive components in particular require careful humidity control to prevent both moisture damage and static discharge.
Military and aerospace applications place some of the strictest demands on desiccant performance. Equipment, electronics, and components stored or shipped under government contracts often must use desiccant packs that meet MIL-D-3464 specifications, which is why molecular sieve and high-quality silica gel desiccants are standard choices for these industries.
Industrial machinery storage is another common application, where desiccant packs help prevent corrosion on metal parts and components during long-term storage or shipment overseas.
Combining Desiccants with Other Protective Packaging
Desiccants can be used within a variety of packaging materials, including boxes or bags. They can be integrated into the packaging material itself or included as separate packets or sachets. For ultimate protection, consider using desiccant combined with a moisture barrier bag, humidity indicator, and/or VCI product.
Pairing desiccant packs with a sealed moisture barrier bag creates a controlled microclimate that keeps humidity low for the duration of storage or transit. Adding a humidity indicator card lets you visually confirm, at a glance, whether the desiccant is still performing or needs to be replaced. For products at risk of corrosion specifically, combining desiccant with a vapor corrosion inhibitor (VCI) product adds an additional layer of protection against rust and oxidation.
How to Choose the Right Desiccant Pack
When selecting a desiccant pack, it helps to work through a few key questions:
- Environment: What humidity and temperature conditions will the product encounter during storage or transit?
- Duration: Is the product being shipped for a few days, or stored for months or years?
- Product type: Is the product sensitive to corrosion, mold, or odor, and does it have any compliance requirements such as MIL-D-3464?
When using desiccants, it is important to choose the right type and amount of material for the specific product being packaged. Too much desiccant may cause the product to become too dry, while too little desiccant may not provide adequate protection. A Royco Packaging product specialist can assist with the selection of the proper products for any moisture control application.