Whether you’re shipping materials to a customer overseas or preparing for a long storage period, desiccants help keep your items safe from rust, mold, mildew and other issues. However, even the best desiccants can fall short if there isn’t enough of them. So, how much desiccant do you need? Let’s take a closer look at desiccant calculations and the desiccant calculator we created to help you determine the right amount.
How Desiccants Work
Before we discuss how much desiccant you need for shipping or storage, let’s first review how desiccants work and what they are. Desiccants are porous materials that “trap” moisture, preventing it from causing rust, mold, and other issues.
Most desiccants are made from clay, silica gel, or calcium chloride. These materials use either adsorption or absorption to remove humidity from the surrounding area. However, these materials have a limited capacity to trap moisture, regardless of whether they use adsorption or absorption. This means that desiccants have a limited lifetime during which they will continue to absorb moisture. Their longevity and effectiveness also depend on the amount of desiccant you use.
How Much Desiccant Do You Need?
How much desiccant you need depends on several factors, including the size of the packaging or container, the amount of empty space within it, the type of packaging or container you’re using, how well the items (such as metal parts) are covered, and more. Since there are many different variables involved, using a calculator to determine how much desiccant you need is helpful. If you’re estimating offhand, here are a few rules of thumb that can help.
How much desiccant do you need:
- Enough to partially cover each layer of your metal parts, if they are layered
- Enough to partially fill empty space in the container
- Enough to distribute the desiccant evenly throughout the space, placing it at the bottom, center, and top of the container
How Much Desiccant and Time
In an experiment testing how long desiccants last, we examined how effective they will be over periods of time when exposed to open air. As you might expect, using more desiccant extended the life of the metal parts. material. Keep in mind that protecting the desiccant and the metal parts in the packaging from the open air will help it last longer.
In general, each amount of desiccant, when exposed to open air, can be expected to last for:
- 1 gram: 30 minutes
- 1 to 5 grams: 1 hour
- 5 to 20 grams: 2 hours
- Over 20 grams: 3 hours
The length of time your metal parts will be in storage or in transit is a key determining factor in the amount of desiccant needed. Remember that the layer of desiccant closest to open air will experience the most exposure. As you can see in the table above from our experiments, the topmost layer of desiccant quickly adsorbed moisture, resulting in a decline in its moisture-trapping capacity over time.
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Amount of Desiccant and Type
When choosing the right amount of desiccant for your application, it’s important to consider not just the volume or surface area of what you are protecting, but also the type of desiccant you’re using. Here’s a breakdown of how the most common types of desiccants work and how much you may need for each.
Silica Gel: Steady Adsorption Rate
Silica gel is one of the most commonly used desiccants and functions through adsorption, which means it holds moisture on its surface rather than absorbing it into its structure. This process allows silica gel to steadily gain moisture over time, maintaining a consistent rate of moisture absorption.
As a result, it wears out at a steady rate, making it a reliable choice for long-term protection. To determine how much silica gel you need, it’s important to consider the environment’s humidity level and the duration of exposure. Generally, silica gel can adsorb about 40% of its weight in moisture, making it suitable for most applications that require consistent protection over time.
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Clay Desiccant: Quick Absorption That Drops Off
Clay desiccant works through adsorption, meaning it pulls moisture into its structure rather than just holding it on the surface. This makes clay particularly effective at gaining moisture quickly, but its rate of adsorption tends to decline over time as the material becomes saturated.
Due to its nature, clay desiccant is ideal for short-term applications or environments with fluctuating moisture levels. However, since clay adsorbs moisture rapidly at first and then slows down, it may not be the best choice for extended periods of protection. You may need to use more clay desiccant compared to silica gel if you require longer-term protection, as its ability to adsorb moisture diminishes as it becomes saturated.
Adsorption vs. Absorption
While both silica gel and clay desiccants are effective, understanding the difference between adsorption and absorption is important when selecting the right type. Adsorption (used by both silica gel and clay) involves moisture adhering to the surface of the desiccant, allowing for more gradual and consistent moisture removal. Absorption refers to a process where a material pulls in and retains moisture within its structure, which tends to saturate more quickly. Recognizing this distinction helps you determine how much desiccant to use, as materials that rely on absorption may saturate more quickly and may require more frequent replacements compared to those that function through adsorption.
In general, the amount of desiccant you need will vary depending on the type, storage conditions, and the nature of the metal parts being protected. Consider factors such as how long you need moisture protection and the environment’s humidity to find the right balance.
