These are Made of high quality aluminum foil, about 16 inch in size, thick and auto-sealing, no leaks, can last for days when inflated. Give Your Big Party A Personalized Presentation With Foil Balloons! This Collection Of Metallic Balloons Features Every Number From Zero To Nine And Alphabets, So You Can Mix And Match To Form Any Number Or Name. Whether You'Re Celebrating A Big Birthday, Graduation Or Anniversary, These Shining Black Foil Number Balloons Are Perfect For Your Celebration. Mix And Match With Coordinating Foil And Latex Balloons, Polka dot balloons & balloon accessories