When you buy a new electronic appliance, shoes, medicines or even some food items, you often find a small paper sachet with the warning: “silica gel, do not eat”.

What exactly is it, is it toxic, and can you use it for anything?

That little sachet is a desiccant – a type of material that removes excess moisture from the air.

It’s important during the transport and storage of a wide range of products because we can’t always control the environment. Humid conditions can cause damage through corrosion, decay, the growth of mould and microorganisms.

This is why manufacturers include sachets with desiccants to make sure you receive the goods in pristine condition.

The most common desiccant is silica gel. The small, hard and translucent beads are made of silicon dioxide (like most sands or quartz) – a hydrophilic or water-loving material. Importantly, the beads are porous on the nano-scale, with pore sizes only 15 times larger than the radius of their atoms.

These pores have a capillary effect, meaning they condense and draw moisture into the bead similar to how trees transport water through the channelled structures in wood.

In addition, sponge-like porosity makes their surface area very large. A single gram of silica gel can have an area of up to...

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