If you have ever opened a pack of seaweed or a box of crackers, you have likely seen a little packet marked with the ominous words “do not eat.” These packets, containing silica gel, are ubiquitous in crispy processed foods but also found in pill containers, pet food, or shoe boxes. In larger quantities, silica gel is used by museums to prevent rusting in metal artifacts and mold in taxidermy. Gigantic amounts of silica are also often mixed into concrete for building projects. So what is silica, and why is it everywhere?
Silica, otherwise known as silicon dioxide, is found naturally in the Earth’s crust. To create beads, silica is mined as raw sand then processed and chemically treated before being mixed with sodium carbonate. This is then heated and combined with acid, turning silica into its desired form, hard glassy beads. Inside these beads, the silica particles are organized in a crucial jelly-like matrix. This allows for a porous structure and massive internal surface area composed of a microscopic network of tunnels. An additional key feature of silica is that the particles in each bead are held together through polar covalent bonds and thus, as every chemistry student knows, attract other polar molecules including water. So, when silica is placed in a humid environment, the water in the air is attracted to the bead’s porous surface where it is then pulled inside the bead. This water is then stored inside the bead’s internal network, which is why even fully saturated silica doesn’t feel wet to the touch. Each grain of silica can hold 40 percent of its own weight in water and therefore a standard size 5g packet can absorb up to 2g of water.
Another useful trait of silica gel beads is that they functionally last forever as they can be dried out in a hot oven and then reused. These abilities, and silica’s prevalence in the Earth’s crust, have made silica the most popular commercial desiccant, a substance that is used to keep things dry, since it began to be mass produced in 1919.
For those wondering, if you did happen to ignore the “do not eat” label, you will most likely be okay. The danger associated with the packets is more of a choking hazard than anything. Even if the silica beads absorbed their standard 2g, your body has so much liquid in it you wouldn’t feel anything. However, some silica beads, especially those used to transport machinery, are coated with cobalt chloride, a toxic compound, which is used to indicate moisture levels. In small amounts it will likely cause nausea and stomach discomfort. In large amounts it causes all issues above to a greater intensity as well as worse problems including blood and organ abnormalities. In totality, while not a snack, it’s hard to deny that these tiny packets do a lot of work.