Air-filled only. No helium required. Balloons do not float. Fast and simple at-home inflation - inflate with enclosed straw and it's ready in 10 minutes Reusable- insert the air blowpipe straw into the valve and squeeze the out of the balloons lightly, fold them up and store them away from direct sunlight. Easy at home assembly and set up. The self-sealing Balloons will arrive uninflated. Simply insert a straw into the plastic valve at the bottom of the letter and slowly blow to inflate Hang Balloons on wall. To put up Balloons, use tape or string to attach the Balloons to the wall or hang from the ceiling size : 17 inch of each letter