LOONBALLOON Music Balloons, 18 inch Music BIRTHDAY, Accent your happy birthday themed party with this 18in. round Musical Birthday foil mylar balloon. The perfect balloon for your happy birthday party, this 18in. 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.