A filament is a very thin thread or wire, often so delicate it looks like a strand of hair.

You've probably seen filaments without realizing it. Inside an old-fashioned incandescent light bulb, that tiny glowing wire is a filament made of a metal called tungsten. When electricity flows through it, the filament heats up to over 4,000 degrees and glows brightly, giving off light. Modern LED bulbs work differently and don't use filaments, which is why they stay cool and last much longer.

Filaments appear throughout nature too. The stamens inside flowers have thin filaments that hold up the pollen-producing parts. Some algae and bacteria grow in long filament chains under a microscope. Even the vast structures of galaxies in space are called filaments because they stretch across the universe in long, thread-like patterns.

Scientists and engineers also create special filaments for 3D printers: thin strands of plastic that melt and layer to build three-dimensional objects. Whether natural or manufactured, what makes something a filament is that combination of being extremely thin yet surprisingly strong for its size.