Party balloons are mostly made of natural latex tapped from rubber trees and can be filled with air, helium, water, or any other suitable liquid or gas. The rubber makes the volume adjustable.
Filling with air is done with the mouth or with a pump.
When rubber balloons are filled with helium so that they float (restrained by ribbons or strings) they can hold their shape for only a few hours. The enclosed air or helium escapes through small pores in the rubber. If helium is used the gas escapes quicker than in the case of air because the helium atoms are much smaller than the nitrogen and oxygen molecules in air.
Even a perfect rubber membrane eventually loses the gas to the outside, and its contents are contaminated by oxygen and nitrogen migrating inward from the outside. The gases in question actually dissolve in the rubber on one side and are released from solution on the other. The process by which a substance or solute migrates from a region of high concentration, through a barrier or membrane, to a region of lower concentration is called diffusion. The inside of balloons can be treated with a special gel (e.g. "Hi Float" brand) which coats the inside of the balloon to reduce the helium leakage, thus increasing float time. Latex rubber balloons are completely biodegradable, but cannot safely be released into the environment: they are a serious hazard to birds and wetland animals that confuse the balloons for food.
Beginning in the early 1990s, some more expensive (and longer-lasting) helium balloons have been made of thin, unstretchable, impermeable metallized nylon films. These balloons are often mistakenly called Mylar balloons. These balloons have attractive shiny reflective surfaces and are often printed with colour pictures and patterns. The most important attributes of metallized nylon for balloons are its light weight, increasing buoyancy and its ability to keep the helium gas from escaping for several weeks. However, there has been some environmental concern, since the metallized nylon does not biodegrade or shred as a rubber balloon does, and a helium balloon released into the atmosphere can travel a long way before finally bursting or deflating. Release of these types of balloons into the atmosphere is harmful to the environment.
Partygoers sometimes entertain each other by untying a balloon and inhaling the helium. Because the speed of sound in helium is about twice that in air, the helium causes the vocal tract to become more responsive to high-pitched sounds and less responsive to lower ones. The result is a voice that sounds high-pitched (and usually very funny).
Balloon artists are entertainers who twist and tie inflated tubular balloons into sculptures (see also balloon animal). The balloons used for balloon sculpture are made of extra-stretchy rubber so that they can be twisted and tied without bursting. Since the pressure required to inflate a balloon is inversely proportional to the diameter of the balloon, these tiny tubular balloons are extremely hard to inflate initially. A pump is usually used to inflate these balloons.
Decorators may use dozens of helium balloons to create balloon sculptures. Usually the round shape of the balloon restricts these to simple arches or walls, but on occasion more ambitious "sculptures" have been attempted with great success. The balloon decorating industry offers everything from simple balloon columns to stunning, very large and detailed sculptures.
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