This is the 7257th most frequent Russian word.
воздушными
"Воздушными" means "air" or "airy" (instrumental plural form, related to air or something light and delicate).
In this sentence, 'воздушными' is used as an adjective to describe 'шарами' (balloons), meaning 'air' or 'airy' in the sense of being related to air.
Мы любовались воздушными шарами в небе.
We admired the air balloons in the sky.
Here, 'воздушными' is employed metaphorically to describe the method of transportation, indicating it was through the air.
Воздушными путями груз доставили на остров.
The cargo was delivered to the island by air routes.
In this instance, 'воздушными' describes 'элементами' (elements), meaning 'airy' or 'light' in a figurative sense of being delicate or elegant.