Well, breasts are less dense than bone or muscle, so it stands to reason they’d float better than the rest of the body. As for why beer bellies and buttocks don’t float, I’d say it’s because of the broader area of attachment. The relatively large area of attachment for a buttock isn’t going to give it much freedom of motion, and it doesn’t float well enough to lift the rest of the body, so it’s held below the water. Same for a beer belly. A breast, though, has a lot more unattached surface area than attached, so it has a lot more freedom of motion.
I see a new and interesting episode of David Letterman’s “Will It Float?” 
What Cat Lady said. BTW I have natural 38DD boobs, and they float horizontally in the water.
Sorry I have no breats to speak of but when I was a good deal heavier (about 50 lbs) I had to use much more weight while scuba(ing), that may be partially due to a bigger wetsuit. But also I could only become negativally boyany if I exhailed all the air I could (non-scuba), now I can become negitive boyuany with about a little more air in my lungs as a normal exhale woule leave. This applies to fresh water only, salt water is more ‘floaty’
Good point. I’ve never been skinnydipping. Maybe I should do this in the interest of science.
Skinny dipping makes all the difference…mine float when there’s no bathing suit to hold them down
And this from someone who might be named after a British warship.
I used to be overly endowed, and I can testify that mine floated. Thanks to a good surgeon, they are much smaller now. They still might, but it’s a lot harder to tell.
If the buoyancy was significant, Carol Wayne would never have drowned. I would guess the actual density of breast tissue varies according to the build of the individual.
Well, back in my single days… the phrase “She’ll never drown” meant that the girl in question was more than adequately endowed…
My sis and I used to go skinny dipping at night. Well almost…we are not very good swimmers so we did wear life jackets 
.
And oh yeah, they do float.
The original life vest was called a Mae West.
Hasn’t anyone learned from history?
Nah, on this subject we prefer to be doomed to repeat it.