A
balloon is a flexible bag that can be inflated with a
gas, such as
helium,
hydrogen,
nitrous oxide,
oxygen, or
air. Modern day balloons are made from materials such as
rubber,
latex,
polychloroprene, or a
nylon fabric, and can come in many colors. Some early balloons were made of dried animal
bladders, such as the
pig bladder. Some balloons are used for decorative purposes, while others are used for practical purposes such as
meteorology,
medical treatment,
military defense, or
transportation. A balloon's properties, including its low
density and low cost, have led to a wide range of applications.