A parachute is a collapsible umbrella-like structure used to retard movement through the air. The parachute was invented in the late-eighteenth century, being used for descent from balloons, and made successively from canvas, silk, and nylon. When opened – either manually by pulling a ripcord or by a line attached to the aircraft – the canopy fills with air, trapping a large air mass which, because of the parachute's movement, is at a higher pressure than that outside, producing a large retarding force. The canopy consists of numerous strong panels sewn together. Parachutes are used for safe descent of paratroops and others, for dropping airplanes or missiles, and returning space capsules. Sport parachuting, or skydiving, has become popular.