Actually, it could be either hydrogen or methane. Both have been used but both are HIGHLY flammable, and methane even MORE dangerous than hydrogen is.
I quote from the article cited below:
With Helium being expensive and now subject to shortage, many people are looking for more available and inexpensive alternatives.
But it surprises me that party balloons sold anywhere in the USA are even ALLOWED to be filled with ANYTHING BUT Helium! Regardless of being more expensive and there being a shortage, if I were a RETAILER, I would not want the chance of a LAWSUIT from the damages, medical or otherwise, which can be so READILY caused by using hydrogen or methane.
Do you remember the old TV show from the 1970's, "Love Boat?" The actor who played, "Gopher," Fred Grandy, had his hands horribly burned by balloons that were filled with hydrogen, and were popped and exploded. I quote from second article below:
But in 1982, a scary accident occurred in a Turkish taxi: A cigarette ignited some balloons that were inexplicably filled with hydrogen, injuring Tewes, Grandy, and several others; Grandy suffered severe burns on his hands and face.
So, there you have it. If I were you, I would try to find out WHERE he got that balloon, and then AVOID getting any future "supplies" from them AT ALL!!! You don't want to mess with that dangerous stuff!
Me… kittyslave23… I know my place.