Kidneys are a filter system. The main job of the kidneys is to remove waste from the blood and return the cleaned blood back to the body. Each minute about one litre of blood ï­ one-fifth of all the blood pumped by the heart - enters the kidneys through the renal arteries.
The volume of helium in the balloon has been estimated as being able to lift a total load, including the balloon material and the structure beneath it, of 65 pounds (29 kg) at sea level and 48 pounds (22 kg) at 8,000 feet (2,400 m).
But the weight of the balloon alone will make it heavier. It therefore makes sense to construct the balloon from the lightest possible material. Rubber is quite heavy but it is also elastic -- thus the air inside is compressed.