Betallic Foil Balloon 15845SB Number 5-Silver Megaloon, 40" Includes self sealing valve - self-sealing valve prevents the gas from escaping after it's inflated. Inflate with helium or air - the balloon can be inflated with a helium Inflator or with air using a balloon air Inflator. Balloon comes uninflated. Mylar/ Foil Balloon.