The practice of putting on absorbent top covers to soak up moist air
seems to work and is basically sound since water vapour is lighter than
air and therefore will rise - all other things being equal.
What about reports then of practices of putting on non
absorbent/insulated top covers. Well at least they will stop the rising
(and probably slightly warm) water vapour from condensing back into
water when it contacts the cold top cover.

Now about other things being equal - If a screened bottom board is used
, the natural drafts caused by passing wind outside the hive, probably
cause enough air currents inside the hive to overcome the gentle upward
rise of the water vapour coming off the cluster, and the water vapour
probably gets flushed out through the screened bottom by these
relatively stronger currents. Having an "open" top or a "closed" top
would make little difference in this case, but if closed it could be
argued that it would be better to be an insulated top rather than not. I
guess extreme cold conditions (well below freezing) maybe also favour
some top insulation.
So the question is - with screened bottoms should the top be open or
close or does it matter.
Alan Riach
Bathgate,Edinburgh