Comparing Commercial Desiccants - Silica Gel, Clay and Molecular Sieve

Desiccants are used to absorb moisture from the air in order to prevent it from harming products like electronics, leather goods, dried food, and vitamins. In order to prevent damage from moisture in the air, desiccants are used to absorb the moisture to keep the air dry. There are three types of commercial desiccants; Silica Gel, Bentonite Clay, and Molecular Sieve. Silica Gel, the highest absorption capacity desiccant available on the market, is found in industrial, commercial and residential settings and has been approved by the Food and Drug Administration (FDA) to be used in dry food packaging. Bentonite Clay is a naturally absorbent material that is used in industrial settings, though not as frequently as Silica Gel. Molecular Sieve desiccant is used in unique situations where moisture control is needed at extremely high temperatures.

Bentonite Clay is a naturally occurring absorbent granular material. Even when fully saturated, Bentonite Clay does not clump and remains dry to the touch. Absorbent up to 120° F (49°C), this desiccant is most effective at 77°F (25°C) and can absorb up to 25% of its weight in moisture. When temperatures rise above 120° F (49°C), Bentonite Clay releases the moisture it has absorbed back into the air. As a result, this desiccant can be reactivated to be reused many times. Tyvek® packaging, which holds in dust better than other packaging material choices, tends to be the preferred packaging for Bentonite Clay since it yields a high amount of dust.

Silica Gel is commonly found packaged with products like electronics and leather goods. A manmade substance, Silica Gel is made synthetically from sodium silicate and is a solid, despite what the name suggests, and is found as small clear beads. Like Bentonite Clay, Silica Gel remains dry to the touch even when it is fully saturated and will not clump or stick. Able to absorb 40% of its weight in moisture, Silica Gel is the most absorbent desiccant available on the market. Silica Gel is most efficient up to 100°F (38°C) but can absorb moisture up to 220°F(104°C). When heated to temperatures between 220-250°F (104-121°C), Silica Gel will release the moisture it has absorbed, thereby reactivating it for reuse. Silica Gel comes in a variety of packaging including cotton, Tyvek®, and perforated clear plastic. Cotton and Tyvek® packets are commonly used in dry food packaging and meet the FDA requirements to be packaged with dry food. Silica Gel packaged in Tyvek® yield practically no dust particle which makes it a good choice for being packaged with dry food or electronic items that could be damaged moisture.

Molecular Sieve desiccant is also a manmade substance. Unlike Silica Gel and Bentonite Clay, this desiccant does not remain dry to the touch. As the Molecular Sieve particles absorb moisture, they lose their dry solid state and become moist to the touch. Of the three types of desiccants, Molecular Sieve has the lowest absorption capacity at only 22% of its weight. Molecular Sieve can absorb effectively at extremely high temperature, being able to absorb moisture up to 450°F (230°C). Due to the change of its physical characteristics and the high temperatures at which it can absorb, Molecular Sieve desiccants cannot be reactivated and reused. Molecular Sieve can be used with electronics due to its low dust yield, but is not approved by the FDA to be packaged with food.

Absorption capacity may well be the primary consideration when choosing a desiccant, Bentonite Clay can absorb 25% of its weight, Silica Gel can absorb 40%, and Molecular Sieve 22%. Bentonite Clay has the highest dust yield of the three, requiring more expensive packaging in order to contain the dust. Silica Gel and Molecular Sieve have a very low dust yield which makes them safe to use with products that could be damaged by dust. There is little concern about Silica Gel packets tearing as the small beads are solid, non-toxic, and are easy to clean up, even when fully saturated. Since Bentonite Clay is a dusty material, in the rare occurrence the packets tear, the dust will cover the products it is meant to protect. Cleaning up saturated Molecular Sieve from a torn packet would also be more difficult than cleaning up beads of Silica Gel. As a result, Silica Gel in Tyvek® packaging is the best choice for applications that require minimal dust.

Bentonite Clay has the smallest optimum temperature range with a top temperature of 120°F (49°C). Molecular Sieve has the highest absorption temperature of the three desiccant types with a top temperature of 450°F (230°C). Silica Gel's range, with a top temperature of 220°F (104°C) means that it can be used for more applications than Bentonite Clay. Bentonite Clay and Silica Gel can both be reactivated by heating the particles so that they release the absorbed moisture while Molecular Sieve desiccants cannot be reactivated. When looking at cost, it is important to look at not only how much the desiccant costs per unit, but also the absorption capacity of the desiccants. With the highest absorption capacity available on the market, a wide optimum temperature range, and the ability to be reactivated, of the three desiccants, Silica Gel is the most widely used desiccant on the market.