Helium is used to fill balloons for many reasons. One of the guiding principles governing liquids and solids is the Archimedes principle. As per this principle, any object is immersed partially or wholly in a liquid, is buoyed up by force equal to the weight of the fluid, displaced by it.
In case the particular object is denser than the displaced fluid, it will sink and stay at the bottom. In case it is lighter than fluid displaced, it will rise (gas) or float (liquid). As regard hot air balloons, they tend to rise because the air within is hot and less dense compared to the air outside.
Just like hot air, helium is lighter than air at ambient temperature. This is the reason why helium balloons rise when they are let loose. This makes them ideal for party decorations as well as weather observatories for scientific studies. For parties, get helium balloons delivered through professionals.
How do they work?
The helium balloons are fundamentally gas balloons that are filled with helium gas. They are the best option as regards the several lighter than air gases which can be used in gas balloons.
Fact is helium is the second lightest element in the universe except hydrogen. Since helium is lighter than air, making it of use in balloons help them to rise in the sky while atmospheric air acts as a fluid.
The density of Helium is less than that of atmospheric air. Speaking specifically, density of air is 1.2g/L while the density of Helium is just 0.1785gm/L. The high density of air is because of its 80% content of nitrogen which is a heavy element.
Other Gases
• Hydrogen
With regard to hydrogen which might be lighter than Helium, it has certain flammability issues which make it tough to handle. Besides, hydrogen is not much lighter than helium. Though the molecular mass of Helium is double than that of Hydrogen, the buoyancy of a balloon is the difference between the density of air outside and gas inside the balloon. In fact, Helium is only 7.5% less buoyant in air, compared to Hydrogen.
• Methane
Methane features half the buoyancy of helium or hydrogen in the atmosphere of the earth. It is cheap and readily available from natural gas. But like hydrogen, it is also flammable. It may be less dangerous as regards some aspects (range of flammability and speed of burning), but it is more harmful in other aspects (per volume energy content). Methane is unsuitable otherwise also because of its lower buoyancy and flammability.
• Water Vapour
This is a much lesser flammable option. It is just slightly less buoyant than Methane at same pressure and temperature. The big problem is that water is liquid at ambient temperatures. It has to be heated to lift anything. But any failure is a potential disaster. Hot air balloons will simply drift down on the failure of the burner, but a hot steam balloon is heading to catastrophe in case water condenses.
• Neon and Ammonia
These have molecular mass like water and methane. Neon is a noble gas like Helium. But it is beset with problems like being more costly and less buoyant than Helium. Ammonia is decidedly less flammable than Methane but is corrosive and toxic.
These are some of the aspects related to helium balloons. For DIY projects to decorate with helium balloons, make use of helium balloon kit which is readily available in the market.
Helium 2 Go 