Wack-A-Pack Self-Inflating Foil Balloons, 2 Packages of 4 8 WHACK A PACK PACKETS = 8 Mini Ballons: Wack the pack and a Happy Birthday balloon self-inflates emerging from the bag! Surprise greeting makes the party fun Perfect for party favors or a little extra for a birthday card Instructions for use: Smack the pack and shake. Then quickly thorw on floor. A chemical reaction of the citric acid, sodium bicarbonate and distilled water will create a small bang and inflate the balloon. Do not puncture or break open. Happy Birthday designs will vary among those shown in pictures here.