There has been a lot of talk of this one pin claiming to make balloons float with out helium. The ingredients that were said to be used were baking soda and distilled vinegar. This would be really exciting if it worked! Unfortunately when I tried it, it did not float but it was fun to see how much my bother and sister loved the chemical reaction occurring with the vinegar and baking soda. This is a great summer activity to do when the kids seem bored, I would consider using a smaller than a 2 liter bottle.
3 table spoons of vinegar
1 teaspoon of baking soda