A balloon is a flexible bag that can be inflated with a gas, such as helium, hydrogen, nitrous oxide, oxygen, and air. For special tasks, balloons can be filled with smoke, liquid water, granular media (e.g. sand, flour or rice), or light sources. Modern day balloons are made from materials such as rubber, latex, polychloroprene, or a nylon fabric, and can come in many different colors. Some early balloons were made of dried animal bladders, such as the pig bladder. Some balloons are used for decorative purposes or entertaining 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. The rubber balloon was invented by Michael Faraday in 1824, during experiments with various gases. He invented them for use in the lab. Applications Play Decoration Balloons are used for decorating birthday parties, weddings, corporate functions, school events, and for other festive gatherings. The artists who use the round balloons to build are called "stackers" and the artists who use pencil balloons to build are called "twisters." Most commonly associated with helium balloon decor, more recently balloon decorators have been moving towards the creation of air-filled balloon decorations due to the non-renewable natural resource of helium limited in supply. The most common types of balloon decor include arches, columns, centerpieces, balloon drops, sculptures, and balloon bouquets. With the increased aptitude for balloon twisting as well as balloon stacking, the rise of the deco-twister manifests itself as the combination of stacking techniques as well as twisting techniques to create unique and interesting balloon decor options. Party Balloons Party balloons are mostly made of a 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. Often the term "party balloon" will refer to a twisting balloon or pencil balloon. These balloons are manipulated to create shapes and figures for parties and events, typically along with entertainment. 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 or plastic balloons are filled with helium so that they float, they typically retain their buoyancy for only a day or so, sometimes longer.