[gentle music] - [Michelle] Hot air balloons might seem like magic, but there's actually some pretty straightforward science behind how they fly.

- Hot air balloon's about as simple as you can get.

You fill a large envelope, what we call the envelope, which is the balloon sitting above us.

You fill it with air laying on the ground and then you take a burner and you heat that air up and hot air rises so as you get that air heated up enough to overtake the weight of the basket and whoever's in it, you'll leave the ground.

- Imagine a bunch of little kids when it's cold, how you all squeeze into the bleachers and you pack in really tight and then when it starts to get hot, somebody turns the thermostat up and the building starts to get warmer and warmer, how you start spreading out and bouncing around.

And the hotter it gets, the more the molecules bounce around.

When they do that, they squish the other molecules out the bottom of the balloon so there's less molecules creating less weight or lift.

And so the balloon rises because there's less molecules on the inside.

- [Michelle] Air temperature and humidity have a lot to do with how much lift you can get on any given day.

- On a very hot, humid day like it's gonna be today I can't lift as much weight as I can on a nice cool day because I'm working on the differential between the heat and the balloon and the outside temperature.

- [Michelle] And the balloons themselves aren't made out of just any old fabric.

They have to be able to withstand a lot of heat and pressure.

- Most all balloons nowadays are nylon and they coat it so it's non-porous so it holds all the heat in so it doesn't flow through the fabric.

- [Michelle] Once a hot air balloon is off the ground, you can't exactly steer it like you would a car or a plane.

- [Mark] We float with the wind.

- [Pete] The balloon goes with whatever air flow it's in, whatever the wind is.

So if the wind is out of the west, you're gonna go east.

However, there are usually differences at different altitudes, slight changes in direction that you can find.

- [Michelle] Air is a fluid and just like a body of water, it has layered currents that are shaped by whatever it's flowing over.

Dark, reflective surfaces, like parking lots, create rising currents of heat while forested areas create cool spots with sinking currents.

Although they can't steer their balloons, balloon pilots can change the direction they're going by rising up or sinking down into an air current that's going the direction they want to travel.

There's even a place in Albuquerque, New Mexico where when the conditions are right, pilots can fly in a box pattern, rising up to ride a current going one direction, then sinking down to go back the way they just came on a different current.

North Carolina is actually a hotspot for hot air ballooning with a rich history of innovation and balloon production.

North Carolinian Tracy Barnes added some important innovations to modern hot air balloon and basket construction.

- He invented the parachute valve for the hot air balloon.

Instead of patenting it, he knew that the safety factor that put into all balloons was greater than any money that he could receive.

So he opened it up to all the other balloonists out there says, "Please use it.

This is my idea, but take it and run with it."

He developed this basket right here and he did different things like he did a weave that was vertical.

So if you rub on something, you catch it, say a wire, a power line, it'll just slide along here and up it goes and it slides right off.

[uplifting music] - [Michelle] Fortunately, knowing the science doesn't take away from the magic of watching hot air balloons fill up as the sun sets.

[uplifting music continues]