[altacc]

The idea of "balloon-grade" led me down a rabbit hole. It seems that there are many defined grades of He with the majority being grade 5 (99.999% purity, 2 steps down from the purest) and the majority of He used, including in balloons is grade 5 due to ease of transporting just one grade. That made it cheaper to use grade 5 for party balloons than artificially reducing the quality.

In the last few years there has been more low quality balloon grade (97.5% purity) produced by refineries in the US, increasing the availability and reducing the cost.

http://www.kornbluthheliumconsulting.com/wp-content/uploads/... https://zephyrsolutions.com/what-are-the-different-grades-of...

[PaulHoule]

Couldn't you just buy high purity helium and mix in some air close to the point of sale?

[mtoner23]

you're not going to save much cost by doing that 99 -> 97% isnt much difference in helium. the difficulty is not in the quantity of helium but the purity. if you dont care much about the purity it will be cheaper to produce.