This year marks the 91st anniversary of the Macy’s Thanksgiving Day Parade. And while the intricately designed floats and talented performers are entertaining to watch, the real reason we tune in each year is to see the enormous, gravity-defying balloons. Have you ever stopped to wonder how these balloons are designed and constructed, and how the creators uses physics and engineering to ensure that the balloons will be a success?

Here are a few facts about the balloons, according to Francie Diep for Popular Science. "The average balloon requires 12,000 cubic feet of helium. That's enough to fill about 2,500 bathtubs. The average balloon requires 90 handlers during the parade. Handlers must weigh at least 120 pounds and have no heart, back, or knee problems. The balloons were originally made of rubber. Now, they're made of fabrics coated in a polyurethane material that's flexible, durable, and leak-resistant. Polyurethanes are synthetic plastic materials that also commonly show up in couch cushions, insulation, and even in synthetic-fiber clothes."

In an article for WIRED, Rhett Allain explores the physics behind the giant balloons. "The balloons used in the Macy’s Day Parade seem to cheat physics in order to move through the sky. Of course, they aren’t cheating physics. It is because of physics that they are able to float.

There is indeed a force pulling down on these massive balloons. This gravitational force is proportional to the mass of the object. Both the outer material and the gas within have mass that results in a weight of perhaps 2,000 Newtons (450 pounds). Yet even with so great a downward force, the balloons stay aloft. There must be an upward force at work on the object. This is buoyancy force, and it is caused by a differential air pressure on the top and bottom of balloon."   

To learn more, read "The Science And Engineering Of Macy's Thanksgiving Day Balloons" from Popular Science and "The Physics of the Macy’s Thanksgiving Day Parade Balloons" from WIRED.