A superpressure balloon is a type of aerostatic balloon in which the balloon’s volume is kept almost constant even when the temperature of the lifting gas changes. Because of this, the balloon is able to remain in a stable altitude for longer periods. In contrast, the variable-volume balloons, which are more common, are only partially filled with the lifting gas, or are made with elastic materials. Here, the lifting gas volume changes due to the heating and cooling in the diurnal cycle (temperature changes in the same day). Superpressure balloons are used in areas where very long duration flights are required, for example, for unmanned scientific experiments in the upper atmosphere.