Types of Desiccants, Compared

Adsorption vs Absorption: The Distinction That Decides Everything

Two mechanisms capture water, and confusing them is the root of most desiccant mistakes. Adsorption is a physical process: water molecules adhere to the vast internal surface of a porous solid through Van der Waals forces. Silica gel, activated clay are adsorbents; they stay solid, do not change chemically, and their capacity is capped by available surface area. Absorption is a chemical process: the desiccant reacts with and dissolves into the water it captures. Calcium chloride is an absorbent; it deliquesces, turning into a brine, and its capacity is governed by how much active material it contains, which is why it reaches up to 300% of its weight (400%+ under optimal conditions) where adsorbents plateau at 25–40%. Magnesium chloride (BENZPACK BE DRY) is also hygroscopic but binds the water into a non-leaching solid rather than a brine.

The second decisive property is the adsorption isotherm, the curve of how much water a desiccant holds at a given relative humidity. Silica gel rises gradually and performs best in the mid-range. Clay sits below silica gel but is cheap and stable. Calcium chloride does the opposite of all of them, its uptake accelerates as RH climbs toward 100%, which is exactly why it dominates the high-humidity, long-voyage container problem. Choosing a desiccant is choosing the isotherm that matches your enclosure's humidity profile.

Why the Cheapest Sachet Is Rarely the Cheapest Shipment

Buyers often compare desiccants on price per unit, which is the wrong number. High-purity calcium chloride such as BE DRY ULTRA absorbs roughly ten times more water than silica gel — a 1 kg calcium chloride unit does the work of around 10 kg of silica gel in a sealed container. Because each unit holds so much more, a container needs far fewer of them, and that cascades into lower freight weight, less installation labour and fewer SKUs to stock. When a single uncontrolled container-rain event can write off cargo worth more than the entire desiccant budget for a year, the meaningful figure is total cost of ownership and the margin of safety, not the line-item price of one bag.

Purity compounds the advantage. Commodity calcium chloride is often around 77% pure; BENZPACK BE DRY ULTRA uses high-purity calcium chloride blended with a modified-starch gelling agent that locks the absorbed water into a solid, leak-proof gel rather than a corrosive brine that can drip onto the load. Silica gel, by contrast, plateaus at about 25–40% of its weight and saturates early on the long, hot routes where protection is needed most. Silica gel is reusable — it can be regenerated by baking — which suits small, repeated in-house packs; calcium chloride is single-use by design, because the chemistry converts it to gel, and that is precisely what makes it the right tool for a one-way ocean voyage.

For the exact quantity your shipment needs, the DIN 55474 desiccant calculator sizes it from your container, cargo and route; as a rule of thumb a 40ft container of hygroscopic cargo needs about 10–12 one-kilogram BE DRY ULTRA units. All BENZPACK desiccants are REACH-registered and 100% DMF-free, the chemical the EU banned from packaging in 2009 and that customs still screen imports for.