Tinfoil is a thin, flexible sheet of metal that can be wrapped around food or other objects. Despite its name, modern tinfoil is almost always made from aluminum, not tin. You've probably seen it in your kitchen: that silvery, crinkly material that comes on a roll and can be torn off to cover leftovers or wrap a sandwich.

Tinfoil works well for storing food because it blocks air, light, and moisture, which helps keep things fresh. It's also heat-resistant, so people use it to cover dishes in the oven or wrap potatoes for baking. When you ball up used tinfoil, it becomes shiny and reflective, which is why kids sometimes use it in craft projects or science experiments about light.

The phrase tinfoil hat refers to a cone-shaped hat someone might jokingly wear, supposedly to block mind-reading rays or similar ideas. When people say someone is wearing a tinfoil hat, they mean that person believes in wild conspiracy theories without good evidence. The image comes from old science fiction stories where characters thought metal could block telepathy or radio waves.