We need to talk about those ubiquitous little packets of poison. You know, the ones that come with shoes and electronics. The ones that say alarming things like “Throw away,” “Do not eat,” and sometimes even “Dangerous.”
The packets usually also say “silica gel,” even though they don’t feel like gel at all.
Perhaps you — or your child — have gotten curious and torn one of those little packets open. Perhaps one of you was surprised to find hard little translucent balls. And one of you was surprised to find they had no flavor and couldn’t be chewed.
So what is this stuff? Is silica gel poisonous?
Let’s start with the silica part
Silica is also known as silicon dioxide. In its natural form it’s called quartz, the second most common mineral on Earth. You may know it better as sand, but gemstones like amethyst and citrine are also forms of quartz.
Silica gel is a synthetic form of quartz that’s made by acidifying sodium silicate. In its liquid form sodium silicate is also known as waterglass. It’s used in detergents, dyes, food preparation and many other products and industrial processes.
Why is it called gel?
Silica gel is technically a xerogel. “Xero-” is the same root word as in Xerox (dry copies) and xerostomia (dry mouth). And yes, it means “dry.” Silica gel is a dry gel.
All gels — toothpaste, pudding, some would say your heart and lungs — start out as tiny particles floating in liquid. Under the right conditions the particles fuse together. They form a 3-D structure that holds the liquid in and gives it shape — even if that shape is a bit squishy.
To make a gel into a xerogel, the liquid is removed. The 3-D structure that’s left behind is lightweight and full of little holes called pores. (Dry silica gel can also be called an aerogel, because its pores are filled with air.)
All air has water in it. In an enclosed space — like a shoe box — water from the air can settle on any surface, causing damage. Silica gel packets adsorb the water and protect whatever they are packed with.
So silica gel absorbs water?
Silica gel adsorbs water. The water molecules cling to the surface of the silica gel, rather than getting inside. Silica gel beads are tiny, but they have millions of microscopic pores. They can hold an enormous number of water molecules.
There’s still a limit to the amount of water silica gel can adsorb, however. Once all the spaces for water molecules are filled it can’t take on any more. Since the water is just hanging on to the outside of the silica gel beads, though, it can be driven off with heat.
But is silica gel poisonous?
Silica gel, like sand, is inert. It doesn’t react chemically with its surroundings. When it’s swallowed it passes through the GI tract and comes out the other end unchanged.
There is one caveat, however. The silica gel that comes in opaque packets is called non-indicating, which means it always looks the same whether or not water is present.
But there’s another kind called indicating silica gel that changes color as the gel becomes saturated with water. Silica gel itself doesn’t change color, because it’s inert. So it has chemicals added to it that do change color.
Blue indicating silica gel has cobalt chloride added. The chemical structure of dry cobalt chloride makes it look blue. It likes water, though, and will let go of its chlorine atoms to make room for water molecules. This change in its chemical structure makes it look pink. If the gel dries out the color returns to blue.
An accidental or experimental taste of blue indicating silica gel is not particularly harmful, but cobalt chloride is generally pretty toxic. It’s gradually being replaced with orange indicating silica gel. This kind uses less toxic methyl violet, which changes from orange to green when it takes on water.
How to dry silica gel packets for re-use
Silica gel will begin releasing the water molecules on its surface when heated to about 220°F. However, the packet that holds the gel is likely to be damaged if heated above 250°F. That gives a pretty narrow temperature range to work with.
Indicating silica gel is dried until it returns to its original color. Non-indicating gel is a little trickier, because you can’t tell when the water has all been driven off. Drying times are approximate.
Note: Never dry or re-use silica gel that has been contaminated with anything other than water!
- Spread the silica gel packets on a baking sheet.
- Place in the oven as far from heating elements as possible.
- Set the temperature to between 220°F and 250°F.
- Allow to dry for between 2 and 24 hours.
How to dry loose silica gel
There are some uses for silica gel that work better with the loose beads. If you have a lot of packets you can always open them and mix the beads together. Without the packaging you can turn the oven up to 300°F and dry them in about 3 hours.
Loose beads can also be microwaved. Indicating silica gel is microwaved at 3-minute intervals until the color changes. Again, it’s hard to say how long to heat non-indicating gel.
Uses for silica gel packets
- Wet cell phone Remove battery, SIM and SD cards and place phone in a bowl or bag filled with silica gel packets for 24 hours
- Razors and razor blades Store in a closed container of gel packets to retard dulling
- Important documents Add packets to file box, drawer or envelope to avoid moisture damage to paper
- Electronics Add packets to camera cases and hearing aid holders
- Gardening seeds Store seed envelopes in a box with gel packets
- Prevent tarnish Add packets to silver drawer and jewelry box
DIY: Make your own silica gel packets
Silica gel beads can be purchased in bulk from many stores. Empty tea bags are easy to find on eBay if you can’t find them elsewhere. Fill the tea bags with the gel and use as desired.
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