That’s right: You may soon be able to use coal to make your car more fuel-efficient. Not by running it on coal — gross! — but building it out of metal mixed with structures found in coal ash.

Fly ash, a byproduct of burning coal, contains microscopic bubbles called cenospheres. They sound like Clive Barker creatures, but they’re actually really useful — because when you mix them with metal, they make the metal lighter without compromising its strength. Even regular gas-powered cars could be at least 10 percent lighter, and thus more fuel-efficient, if they were made out of cenosphere-infused metal. The savings are even greater for electric cars, because the battery also could be made at least 20 or 30 percent lighter.