Creation of Japanese Balloon Bombs
In a paper titled, "How Geologists Unraveled the Mystery of Japanese
Vengeance Balloon Bombs in World War II," J. David Rogers, Ph.D. does a good job of explaining how the Japanese Balloon Bombs worked.
"...The balloons were crafted from mulberry paper, glued together with potato flour and filled with expansive hydrogen. They were 33 feet in diameter and could lift approximately 1,000 pounds, but the deadly portion of their cargo was a 33-lb anti-personnel fragmentation bomb, attached to a 64–foot long fuse that was intended to burn for 82 minutes before detonating. The Japanese programmed the balloons to release hydrogen if they ascended to over 38,000 feet and to drop pairs of sand filled ballast bags if the balloon dropped below 30,000 feet, using an onboard altimeter. Three-dozen sand-filled ballast bags were hung from a 4-spoke aluminum wheel that was suspended beneath the balloon, along with the bomb. Each ballast bag weighed between 3 and 7 pounds. The bags were programmed to be released in pairs on opposing sides of the wheel so the balloon would not be tipped to one side or another, releasing any of the precious hydrogen. In this way the balloons would rise in the daylight heat each day of the crossing and fall each evening, till their ballast bags were depleted, at which time the balloon and its deadly contents would descend upon whatever lay beneath it..."
Here's a diagram that outlines the different parts of the Japanese balloon bomb: