Ferrofluid is made of tiny, nanometer‐sized particles of coated magnetite suspended in liquid. When there’s no magnet around, ferrofluid acts like a liquid. The magnetite particles move freely in the fluid. But when there’s a magnet nearby, the particles are temporarily magnetized. They form structures within the fluid, causing the ferrofluid to act more like a solid. When the magnet is removed, the particles are demagnetized and ferrofluid acts like a liquid again.