Re: Why are ice cubes in the bottom tray of 2 trays more difficult to remove?

I have been giving your question a lot of thought.  I would have tried an 
experiment or two but I have no ice cube trays at the moment - I seem to 
have forgotten them during my recent move.  In any case, I think there are 
two factors involved in the behavior you are seeing.  First, I 
believe sublimation (the direct evaporation of ice) could be playing a 
small role in making the cubes in the upper tray easier to remove than 
those in the lower.  Have you noticed that the cubes in the top tray tend 
to be slightly smaller than the ones in the lower?  Those good old 
frost-free freezers "eat" ice cubes as well over time.  I have always found 
smaller cubes a bit easier to remove than the bigger ones.

Also, our tendency is to remove the cubes in the top tray first, then work 
on the lower tray.  During that brief time, the cubes in the lower tray 
have a chance to warm up and melt on the surface.  The small layer of 
liquid that forms between the ice and the tray wall makes it more difficult 
to remove the cube.  The thin film of water clings to the ice, acting 
almost like an adhesive.  I suggest you try taking both trays out of the 
freezer at the same time, but taking the cubes out of the bottom tray 
first.  See if the behavior you normally observe is reversed.  Sorry I 
can't test it out myself - I haven't had time to shop for ice cube trays 
yet.

Anyway, good luck with your test and thanks for the question.

Kieran