Before doing any demonstration with liquid nitrogen see the Liquid Nitrogen Safety Page

Shrinking Balloons

Materials: ice chest, balloons

This is a very popular one. Blow up a balloon and ask the students how many balloons can fit into the ice chest. Take some responses. Have students inflate some balloons for you at least 10 or so. Pour some liquid nitrogen into the ice chest. With gloves begin taking balloons and putting them into the ice chest. As they get down into the nitrogen it is best to use tongs to push them all the way down.

As the nitrogen cools the air in the balloons the air molecules slow down their movement and the balloon begins to shrink. Many kids will think that the air has left the balloon. As you begin to fill the ice chest with balloons the first ones in will shrink but the next layer or so may need to have nitrogen poured over them. Be careful, if the balloons are sticking up over the top of the ice chest some of the poured nitrogen will spill outside the chest. So it is best to add more nitrogen before the balloons begin to pile up.

Once you have added enough balloons to the chest you can begin to take them out. Only use tongs to remove the balloons. The balloon will begin to re-inflate immediately as you take it out of the ice chest and moments after you have pulled out a balloon it is completely safe to touch and shortly after looks and behaves like a normal balloon.

Repeated freeze/thaw combinations will be more than most balloons can handle and some will pop on the re-inflating.