A balloon is an inflatable flexible bag filled with a type of gas, such as helium, hydrogen, nitrous oxide or air. Modern balloons can be made from materials such as rubber, latex, polychloroprene, or a nylon fabric, while some early balloons were sometimes made of dried animal bladders. 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.
http://en.wikipedia.org/wiki/Balloon
