OK, I know it is a bizarre question, but I am reading Dexter in The Dark and the question came up. The majority of the police characters believe that a head will float, while one of them maintains it will sink. So now I’m curious.
Well, a human head washed up in Scotland the other day, but it was in a plastic bag which may have given it extra buoyancy…
I´m WAGing here, but I´d say it would sink. If memory serves me well the average noggin comes in at around 5 kilos… but before going to the bathroom to plunge my head in the sink and see how much water it displaces.
An average human floats in the water by the air in the lungs, fill them with water and it sinks. A severed head, I suppose has if not the same even greater density than the whole body average, more bone up there, so without any air pocket to provide extra buoyancy it would sink.
I presume that a severed head wouldn´t hold air inside the mouth and sinusoidal cavities for much, but if you plug up the trachea and nostrils and glue shut the lips it´ll maybe float.
The brain contains a significant proportion of fat though…
True, but there’s a lot of skull there. And the skull contains some of the densest bone matter in the body (the temporal bone IIRC).
Somw time after death (depending upon circumstances and temperature), the head will start to decay, and decomposition gases from the bacteria will cause the tuissues to bloat, causing the eyes to bulge out and the tongue to protrude. Under these circumstances, the head will definitely float. (I don’t know if it will float before the bloating. My guess is “no”, but that’s only a guess. I have no experience. I welcome volunteers who wish to expand our knowledge.) It doesn’t matter if the mouth is open or the sinuses have access to the outside – the head isn’t one big gasbag; the individual pockets of tissue will expand on their own.
I learned all this while researching my book. Forensics experts I talked to informed me that the head can easily separate from the rest of the body during decomposition, and can commonly be found by itself in the case of death in a body of water.
Bodies initially sink, usually head first. After a few days, they float back to the surface due to decomposition gasses. If left in the water, the tissue breaks down enough to release the trapped gases, so it sinks again, staying on the bottom.
A head is quite solid, so would sink initially, but like the rest of the body, would come back to the surface as the cavity filled with decomp gas. That said, because it is more dense than other body parts, it would probably float just below the surface. It probably wouldn’t be obvious unless it washed ashore.
Bill O’Reilly being the principal exception.
I feel some particularly macabre sequential threads coming up.
I can’t believe I remembered this slightly gruesome news story from 2006:
I’m thinking CalMeacham is most right here. The body will decompose and gather up gases to the point where the head will float.
And now, I’ll be having some nicely macabre and horrific dreams for the following days with little desire to eat anything that resembles the spherical shape of a head 
I’d really love to see David Letterman tackle this one in the next installment of “Will it Float?”.
Checks list: wood, bread, apples, very small rocks, cider, great gravy, cherries, mud, churches, lead, and a duck.
Shouldn’t float, no.
If Garbrielle were here, I bet she’d try it out for us.
(Okay, not really, but she did measure that eye socket once.)
“The specific gravity of human head averages about 1.097. g/cm”
Tözeren, A. 2000
“Impulse and Momentum: Impulsive Forces and Crash Mechanics”
in "Human Body Dynamics"Springer, New York
Question answered.
It depends whether the mouth is open or closed, surely.
Especially if he did so with Paul Shaffer’s head.
“Anybody else feel like asking me for a fucking raise?”
<Morticia> Children, if you want to learn new things, you must not be afraid to experiment.</Morticia>
Well she did tell us that a head comes in at about 10 pounds, if I recall.
Figure a volume of roughly 12"X6"X9" = 648 cubic inches @ 10 pounds would be a density of 10/648 = 0.0154 lb/in[sup]3[/sup]. Water is 0.0360 lb/in[sup]3[/sup] (at 77 degrees Fahrenheit), which is heavier by double. So unless my estimated volume or weight is grossly incorrect, the head will float.
This cite (PDF) gives a general head volume of 4032.7 cm[sup]3[/sup], which is 246.1 inch[sup]3[/sup]. So…it seems I was indeed a bit off in my estimate. So doing that all over again and assuming a 10-12 pound range:
10/246.1 = 0.0406
12/246.1 = 0.0488
Either of which is denser than water. Though as others have noted, build-up of gasses could change this.