Are 18″, oversized or helium shaped foil balloons self-sealing?
All foil balloons 18" and larger are manufactured with self sealing valves inside. A self sealing balloon valve is a very simple concept of two pieces of plastic heat sealed lengthwise allowing air to flow through the valve. The opening is at both ends. It closes by itself because when there is no air pressure to open the valve it closes. There is no glue or anything like that inside the balloon. Next time you have a mylar balloon cut it open and look at the valve. You will see how simple it is.