After a helium-filled balloon is released, it rises through the atmosphere at a little under two metres per second.  Both atmospheric pressure and temperature drop as altitude increases.  The balloon rises to a height of about 28,000 feet (about 8.4 kilometres) over a period of about 90 minutes.  At that altitude the temperature is about 40 degrees C below zero and the balloon has expanded to reach its elastic limit.  A 27-centimetre balloon elongates, on average, to about 700% of its original, uninflated, size before bursting. 

Under these high altitude conditions, the balloon actually shatters and undergoes what is called a “brittle fracture”.  The resulting pieces of rubber are about the size of a ten or twenty-cent piece and these float back to earth and are scatted over a wide area.  The vast majority of balloons will have this fate. 

It’s at this point, a balloon completes the last part of its life cycle.  The rubber pieces continue to biodegrade (a process which begins, incidentally, from the moment a balloon is manufactured) until it has totally disappeared. 

The time taken varies, but on average, the process of decay for latex runs at about the same speed as that of an oak leaf after Autumn (tests conducted using American conditions). 

A helium-filled balloon which has shattered at altitude will biodegrade much faster than a whole balloon which is simply disposed of in landfill waste.  However, no matter what the environment, a latex balloon decays from the moment its manufacture is completed. 

An American study estimated that well under five per cent of balloons released will not rise high enough to rupture. However, even assuming a less conservative estimate of 10%, the density of balloons on the ground after a mass release would be fewer than one balloon in more 38 square kilometres for every 500 balloons released

There is simply no basis for any fear that animals and fish are consuming either whole balloons or pieces of latex rubber from mass release balloons, or that balloons are having an adverse effect on wildlife.