A solid that’s up to 99 percent gas, it is rigid to a light touch, soft to a stronger one, and shatters like glass if it’s put under too much pressure too quickly; it’s one of the most enigmatic of materials, as well as one of the most versatile.

It can withstand the heat of a direct flame; engineers use it for insulation on oil rigs and for warmth in the insoles of hiking boots worn in the coldest temperatures on Earth. NASA uses it to trap comet dust blowing through the universe at six kilometers per second.
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Nicknamed “frozen smoke” after its ethereal appearance, aerogel is neither frozen nor smoke. It’s also surprisingly low tech—it’s been known since 1931
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Together, these ingredients can form a structure that chemically resembles glass but is so full of whorls and crevices that one cubic centimeter has a total surface area equal to a football field’s. The lightest-weight solid in the world, aerogel weighs 1.2 milligrams per cubic centimeter—barely more than the air molecules around it. In fact, the material itself is almost entirely made of air, like a sponge that consists mostly of holes. Don’t let its lightness fool you: it’s strong. NASA photos show two grams of the material easily supporting a 2.5-kilogram brick.
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And because the aerogels pack an enormous surface area into a tiny volume, small pieces can clear out many liters of water. Kanatzidis’s aerogels sopped up so much mercury that they diluted a solution of 645 parts per million down to 0.04 parts per million. They had similar effects on lead and cadmium, two other pollutants.

The new aerogels aren’t ready for widespread use: they’re made with platinum, so they’re extraordinarily expensive. But if other metals can be used to make them instead (Kanatzidis says they can), chunks of them could be dropped into polluted water, removing contaminants.