Hot air balloons in Spokane are considered to be the oldest successful human-carrying aircrafts. Such air-crafts can propel through air and do not necessarily require being pushed along by the wind. The basic structure of hot air balloons is composed of envelope and a gondola or a wicker basket or a capsule. The envelope is a bag-like structure that contains heated air and the capsule carries a heat source & passengers. The heated air inside the envelope, being of lower density than the comparatively colder air of the surrounding, is responsible for making it buoyant. The envelope is made of nylon with the mouth closest to the heat source, being made from fire-resistant material. In Spokane hot air balloons are popular for many commercial, recreational as well as non-commercial purposes.