There are two geodesic dome structures called “lungs”. The lungs contain large diaphrams that expand and contract with shifts in atmospheric volume/pressure. Otherwise, the warming and expansion of air during the day could blow out glass panes or break the seals on Biosphere 2. The lungs’ total volume capacity is 1.7 million cubic feet (50,000 cubic meters).

The diaphrams are large rubber membranes with a metal disk in the middle which weighs several tons.

Being able to walk inside one of lungs was one the best parts of the tour.