Helium isn’t just for balloons. It’s a valuable technology resource.

Kids may know that balloons are bad for wildlife. This is because, when it’s filled with helium, a balloon can travel many miles into the sky before it loses the ability to float. When it falls back to Earth, the string, rubber or Mylar becomes a hazard for birds, turtles and many other creatures that can become tangled in or choke on what they mistake for a tasty treat.

But many people don’t realize that there’s another reason to hang onto those balloons: The helium inside is a rare resource.

“I think that one of the coolest things is that helium is the second-most abundant element in the entire universe, but ironically, on planet Earth, we only have very, very small amounts,” said Santiago Toledo, a chemist at American University in Washington, D.C.

This is true for a few reasons. For example, helium atoms don’t like to make bonds with other elements or even themselves. This results in them having a very low density – much lower than the density of the particles that make up air, Toledo said.

So when you force a bunch of helium into an enclosed space, such as a balloon, that low density allows the helium to rise above the heavier air around it. This is why helium balloons float.

It’s also why Earth has so little of the stuff, he said. Most of the planet’s helium is locked away underground, usually as a mixture with natural gas, said Toledo. But any time helium is exposed to open air, it will disappear into space.

This is kind of bad news, because helium has lots of uses beyond birthday party decorations. While most of us know it as a gas, helium becomes a liquid at extremely cold temperatures.

“We’re talking about temperatures that are just about what is called ‘absolute zero,’ which is the coldest anything can be in the universe,” Toledo said. Because of this quirk, scientists use liquid helium to keep many types of instruments ice-cold.

If you’ve ever had to get a medical test called an MRI, or magnetic resonance imaging, helium was there to cool the superconducting magnets that make the machines work. In addition, helium is important for creating digital devices such as smartphones, as well as the fiber-optic cables that give us the internet. Helium is also necessary to make sure NASA’s rockets work properly and is an important part of machines called magnetometers, which help the U.S. military detect enemy submarines.

The good news, said Toledo, is that balloons don’t contain only helium, but instead a mixture of lightweight gases. Yet when he sees one get loose into the sky, all he can think about is how a precious resource is just floating up, up and away.