A balloon is a flexible bag filled with a type of gas, such as helium, hydrogen, nitrous oxide or air. Early balloons were made of dried animal bladders. Modern balloons can be made from materials such as rubber, latex, polychloroprene or a nylon fabric. Some balloons are purely decorative, while others are used for specific purposes such as meteorology, medical treatment, military defense, or transportation. A balloon's properties, including its low density and relatively low cost, have led to a wide range of applications.
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's elasticity makes the volume adjustable.
Filling the balloon with air can be done with the mouth, a manual or electric inflater (such as a hand pump), or with a source of compressed gas.
When rubber balloons are filled with helium so that they float, they typically retain their buoyancy for only a day or so. The enclosed helium atoms escape through small pores in the latex which are larger than the helium atoms. Balloons filled with air usually hold their size and shape much longer.
Even a perfect rubber balloon eventually loses the gas to the outside. 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 (for instance, the polymer solution sold under the "Hi Float" brand) which coats the inside of the balloon to reduce the helium leakage, thus increasing float time to a week or longer.
Beginning in the late 1970s, some more expensive (and longer-lasting) foil balloons have been made of thin, unstretchable, less permeable metalized plastic films. These balloons have attractive shiny reflective surfaces and are often printed with color pictures and patterns for gifts and parties. The most important attribute of metalized nylon for balloons is its light weight, increasing buoyancy and its ability to keep the helium gas from escaping for several weeks.
Professional balloon party decorators use electronic equipment to enable the exact amount of helium to fill the balloon. For non-floating balloons air inflators are used. Professional quality balloons are used, which differ from most retail packet balloons by being larger in size and made from 100% biodegradable latex.
Decorators may use hundreds 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. It is also common to use balloons as tables decorations for celebratory events. Table decorations normally appear with 3 or 5 balloons on each bouquet. Ribbon is curled and added with a weight to keep the balloons from floating away.
Large balloons filled with hot air or buoyant gas have been used as flying machines since the 18th century. The earliest flights were made with hot air balloons using air heated with a flame, or hydrogen; later, helium was used.
Balloon catheters are catheters that have balloons at their tip to keep them from slipping out. For example, the balloon of a Foley catheter is inflated when the catheter is inserted into the urinary bladder and secures its position.
There has been some environmental concern over metalized nylon ballons, as they don't biodegrade or shred as rubber balloons do, 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 considered harmful to the environment. This type of balloon can also conduct electricity on its surface and released foil balloons can become entangled in power lines and cause power outages.
Released balloons can land almost anywhere, including on nature preserves or other areas where they pose a serious hazard to animals through ingestion or entanglement. Latex balloons are especially dangerous to marine life because latex retains its elasticity for 12 months or more when exposed to sea water rather than air. Because of the harm to wildlife and the effect of litter on the environment, some jurisdictions even legislate to control mass balloon releases. Legislation proposed in Maryland, USA was named after Inky, a pygmy sperm whale who needed 6 operations after swallowing debris, the largest piece of which was a mylar balloon.