All balloons must be filled with a lighter-than-air gas, typically helium or hydrogen. In the USA, most balloonists typically use helium due to its commercial availability and safety. Hydrogen is cheaper and can give more lift due to its lower density--however, hydrogen is flammable and must be handled with extreme care. We recommend a hydrogen safety class (such as http://www.h2labsafety.org/) if you choose to go this route.
Helium can be bought by a number of local suppliers, such as AirGas, Praxair, or Matheson Trigas. Depending on the quantity, you can get one of your own high pressure containers filled or use one of theirs. Helium is typically stored in high pressure containers like k-cylinders (shown above). Note that helium you can get from a party store is actually mostly Nitrogen which is why we suggest finding helium that is 99%+ purity. Welding shops often have helium to loan or sell as well. For a beginner’s 200g, 20ft balloon we recommend about 200-300 cubic feet of helium (sorry for the units!).
A good way to tell if your balloon is full enough is to simulate your payload with a water jug. Once you have your entire payload set and ready to go: weigh it, your parachute, and your tether cords/rigging, etc. Fill up a water jug with that weight of water, and then add about 8-16 ounces more. If you want more altitude, do less (longer flight time). If you want a better ascent rate, fill it up more. When you're filling the balloon with gas, tie the water jug to the neck of the balloon. Once it is able to just (but completely) lift the jug, you're ready to go. Then, take off the jug (while holding onto the balloon!) and replace it with your payload!
Don’t forget that you need a way to move the helium from your tank into your balloon! You can either purchase a balloon inflation tube from a supplier, or build your own using pipe tubing and valves from home depot. When building your own, the main attributes to think about are:
- The fittings must be able to adapt to the tank outlet
- There is usually a shut-off valve that can limit the flow of gas
- There must be a flexible (and rather long) tube that can transport
the gas from the cylinder into the neck of the balloon
Useful References for Balloon Inflation
Suggested Gas Suppliers
Suggested Inflation Tube Suppliers