Wadding

Wadding is a disc of material used in guns to seal gas behind a projectile or to separate powder from shot.

Wadding can be crucial to a gun's efficiency, since any gas that leaks past a projectile as it is being fired is wasted. A harder or more carefully designed item which serves this purpose is often called a sabot. Wadding for muzzleloaders is typically a small piece of cloth, or paper wrapping from the cartridge.

Model rockets
Wadding is also used in model rockets to prevent the parachute from melting when it ejects. Without the recovery wadding the parachute would melt because the ejection is by a small solid-fuel engine. It gets so hot it melts hot glue almost immediately.

Trivia

 * The father of Robert Morris, "Financier of the American Revolution," died as the result of being wounded by the wadding of a ship's gun that was fired in his honor.