Hydrogen or helium are used. As they are lighter than air that's why they float in air when filled in a balloon.
Also, sometimes oxygen and carbon dioxide from your lungs, if you blew the balloon up with your mouth.
air and helium
hydrogen gas
There are several gases commonly used for filling balloons, with the most popular being helium and air. Helium is lighter than air, allowing balloons to float, while air is typically used for ground decorations. Other gases like hydrogen can also be used, but due to its flammability, it is less common. In total, the primary gases for balloons are helium, air, and sometimes hydrogen, along with other specialty gases for specific effects.
The two types of air balloons are * One is lifted using heated gases. * Another one is lifted using unheated gases.
9 gases in a balloon
light bulbs - neon balloons - heilum
Noble gases are lighter than air. Hence balloons filled with noble gases will float in air.
Hydrogen, Helium
Two of the gases that are used to fly balloons are Hydrogen and Helium. Helium is the preferred gas because Hydrogen is very explosive. The Hindenburg disaster was caused by the ignition of the Hydrogen gas that filled it.
Balloons get smaller over time due to the slow escape of the gases inside the balloon, primarily helium or air. The molecules of these gases are small enough to pass through the porous surface of the balloon material, leading to deflation.
Heated air, like what you breath.
Gases used are: air (and hot air), helium.