Let’s say Abigail* wanted to reach neutral buoyancy by inflating her breasts with helium. If Abigail weighs about 160 lbs and each inflated breast supports 80 lbs, then she would need approximately 35000 L of helium per breast. That would make each breast about 13 ft (4 m) in diameter, or about twice her height. Those ... will be some very VERY big balloon breasts! :D~

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*Abigail is an inflatable female afghan hound character of mine.