LoonBalloon Gender REVEAL Large Question Mark Party BABY Shower BOY or GIRL Mylar BALLOON, SuperShape XL. Accent your baby shower themed party with this 28in. large unique shape Gender Reveal foil mylar balloon. The perfect balloon for your baby shower party, this 28in. party balloon is great for setting the scene! This balloon includes a self-sealing valve, preventing the gas from escaping after it’s inflated. The balloon can be inflated with helium to float or with a balloon air inflator. Balloon arrives uninflated. Gender Reveal Foil Mylar Balloon 28in.