During a balloon release, the majority of balloons will rise to an altitude of approximately 5 miles. At the altitude, the balloon will either freeze and become brittle or explode due decreased air pressure and the helium expanding. This means that the balloon is reduced to pieces of natural rubber about the size of a penny which fall back to earth where they finish decomposing naturally. Balloons should NEVER be released with anything more than a race card (if applicable). Strings, ribbon, valves, sealing discs and clips are non-biodegradable and may harm wildlife.