The two films at the end of the balloon are in the shape of a long strip, with a length between 10 and 20 cm. The two sides are pressed together and are usually in a bonded state. When the balloon is inflated, the airflow passes through the middle of the film to prop up the film, and the inflation is over. Afterwards, because the internal pressure of the balloon is greater than the external atmospheric pressure, the film is pressed back to the bonding state.
