Science at Home

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Hot Air Balloon

See what happens when air is heated as you make and fly a huge hot-air balloon.

Safety note: Use care when using the heat gun.


  • 30 sheets of tissue paper (22" by 28" each)
  • File folders or poster board
  • Hot air gun (note: hair dryers don't usually get hot enough)
  • Pipe cleaners
  • String
  • Glue stick
  • Tape
  • Scissors
  • Ruler
  • Pen or pencil
  • Template (PDF)


  1. Make the template. You can glue file folders or poster boards together to make your template large enough. Cut out the template along the dotted lines.
  2. Glue sheets of tissue paper together to make 10 panels that measure 7 feet by 22 inches. You'll need three sheets of paper for each panel, glued along the 22-inch edges.
  3. Stack all 10 panels on top of each other. Put the template on top and trace around it (a pencil works best because the tissue paper is so thin). Cut out all 10 layers at once.
  4. Slide the top panel on the pile about a half inch to the left. A portion of the second panel will be showing. Carefully fold the portion of the second panel that's showing over the edge of the top panel. Glue the panels together along this edge.
  5. Now slide the attached first and second panels about a half inch to the right, the opposite way you slid the first panel. Fold the portion of the third panel that's showing over the edge of the second panel and glue them together. BE CAREFUL NOT TO GLUE PANEL THREE TO THE FREE EDGE OF THE TOP PANEL. The left edge of the top panel must remain free.
  6. Continue sliding, folding and gluing each panel. Alternate sliding the panels to the left, then the right, creating an accordian fold as you glue the panels together. Continue until the only free edges are on the first and 10th panels.
  7. Glue the edges of the first and 10th panels together.
  8. Gather about 6 inches of the top of the balloon (the pointy ends) and tie them securely together with string.
  9. Use the pipe cleaner to make a loop that will fit in the base of the balloon. Secure the loop in the base of the balloon by folding about an inch of tissue over the loop and using glue or pieces of tape to hold the loop in place.
  10. Use a hot air gun to inflate the balloon. (Hair dryers don't usually get hot enough.) As the balloon is inflating, look for and glue any gaps that may appear in the seams. Clear tape can also be used to patch small holes. Safety note: Use care when using the heat gun.

What's happening?

When the air inside the balloon is heated, the molecules in the air begin to move around and spread out, and the air becomes less dense. The surrounding, colder air falls beneath the hot air. This forces the warm air upward, which pushes the balloon up with it. The moving warm air creates a convection current.


Convection current
Air or liquid moving from place to place while carrying heat

Thermal energy
The movement of the molecules that make up an object

Background information

The more thermal energy an object has, the faster its molecules move. These moving molecules bump into each other more often as the thermal energy increases. Imagine children standing in a sandbox. If they begin bumping into each other, they will spread out and require more space. This is what happens when molecules get more energy and start moving around – they spread out, thus decreasing the density of the substance. 

Convection is one of the ways heat is transferred from place to place. Convection is the transfer of heat by the movement of warmed matter, especially liquids and gasses. As a liquid or gas moves from one location to another, it carries heat along with it in a convection current. Due to their lower density, heated fluids (such as water or air) rise and cooled fluids fall. When air is heated, the molecules in the air begin to spread out and the air becomes less dense than the surrounding air. The more dense air falls beneath the hot air, forcing the warm air upward.