Cluster ballooning is an extreme sport and a form of ballooning where a harness attaches a balloonist to a cluster of helium-inflated rubber balloons.
Unlike traditional hot-air balloons, where a single large balloon is equipped with vents enabling altitude control, cluster balloons are multiple, small, readily available and individually sealed balloons. To control flight, arrest a climb or initiate a descent, the pilot incrementally jettisons or deflates balloons. Ballast, e.g., bottled water, can also be jettisoned to facilitate ascent.