I seem to recall that the idea of significant reduction in cell size due
to cocoon build-up has been debunked.  Apparently the bees do remove the
cocoons
from cells and the wall thickness does not increase significantly from
this
cause.  Having said that, though I am aware of old dark brood combs
that are tough enough to withstand being stepped on. I notice that the
coping is heavier, but does anyone have a study about actual wall
thickness measurements and dissection?

Allen,
If my memory serves me correct, E.Wedmore in "A Manual of Beekeeping"
states figures regarding the changes in thickness of cell walls over a
period of time. Can't be more precise than that as my copy is with a
beekeeper in England!
He also mentions that any bees produced in cells of larger size than the
"normal" are larger but individually weigh less than their "normal"
counterparts. Hopefully somebody having the above text can check if this
ref. is correct!!
Also, in Beekeeping study notes (modules 5,6,7 and 8) - J.D.and B.D.
Yates quote "According to Dadant, the thickness of the wall of newly
built comb is approx. 0.0025in. thick and in naturally drawn comb
without the use of foundation, the base is 0.0035in. thick; Hooper gives
0.006in. for the cell wall thickness and Winston 0.073mm (0.003in.)."
page 72.

Peter