Leonardo da Vinci proposed linen for the surface of his aerial screw.
The aerial screw drawing shows a helical structure that Leonardo believed could generate lift by rotating through the air. His notes describe a framework covered with a light material, commonly translated as linen. Linen was widely available in Renaissance Europe and could provide a relatively light fabric surface.
The choice illustrates both the ingenuity and the limits of the design. A fabric-covered screw might have been light enough to reduce the machine’s mass, but the available human-powered mechanisms could not produce the speed and power needed for sustained flight. The structure would also have required exceptional rigidity.
The aerial screw is sometimes called a helicopter prototype, but it was not a helicopter in the engineering sense. Leonardo’s idea anticipated the general concept of rotary lift while lacking the power source, controls, and materials required for practical flight.