Blow up the balloon, tie a knot to seal the opening, and then rub it on your sweater for a while. Send them to the ceiling, where they can stay for hours.

"Principle": By friction, the balloon is charged with static electricity, that is, it receives tiny negative electrons on the sweater. The charged balloon sticks to the ceiling because its negative electrode and the positive electrode of the ceiling attract each other. Electrons move on the ceiling until the positive and negative balance. Because the ceiling is not a good conductor, it can last for several hours under the dry and warm indoor temperature before the balloon falls.