Hi, i looked up some data points about helium.
This table gives floating times for helium balloons and the pressure in usual helium cylinders (200 bar). https://de.wikipedia.org/wiki/Luftballon#Ma%C3%9Fe The numbers of fillings per ballon diameter in the "10 liter" column indicate that the carnies fill them sparsely and that there is not much pressure in them. A german trumpet player player forum mentions that the maximum pressure by human lungs is about 1.15 bar (versus 1.0 bar of environmental air pressure). So i guess a freshly filled toy ballon has 1.1 bar. Such a rubber ballon loses most of its helium within 12 hours. I still remember how disappointingly wrinkled they get. Physical theory says that diffusion is proportional to partial pressure. Gene mentions 7200 psi which is about 500 bar. That's about 450 times the pressure in a toy balloon and 2.5 times the pressure in a commercial helium cylinder, which surely does not have 2 inches of wall thickness. https://en.wikipedia.org/wiki/Helium#Gas_and_plasma_phases states "[...] helium diffuses through solids at a rate three times that of air and around 65% that of hydrogen" referring to Hampel, Clifford A. (1968). The Encyclopedia of the Chemical Elements. All in all i riddle what physical (or criminal ?) effect caused the loss of 20 percent (5800 / 7200 = 0.805) of the stored helium's pressure within 12 hours. The only idea i have would be loss of temperature and not loss of substance. The equation for ideal gases is: P * V = n * R * T Volume V and R are constants. Pressure P decreases. So number of moles n or temperature T must have decreased. Have a nice day :) Thomas
