According to Rat, Balloons usually fly. They break off from a larger being called Balloon Legios, and can henceforth freely float in the sky.

If you see a strangely colored object in the sky, it is probably a Balloon Legios.

Though Balloon Legion rarely come to the ground, the numerous Balloons born from come down quite often.

They become completely independent after separating from the Legios. c151