High-altitude balloons are large balloons filled with helium or hydrogen that can reach altitudes of 20 miles or more. They are often used for scientific research, weather monitoring, and testing equipment in the upper atmosphere. These balloons can carry instruments and cameras to collect data about atmospheric conditions, radiation levels, and other environmental factors. Once released, high-altitude balloons ascend slowly until they reach a point where the surrounding air pressure is too low, causing them to expand and eventually burst. The payload then descends back to Earth via a parachute, allowing researchers to retrieve valuable information and materials for analysis.