wrote on Apr 18^th, 2011 at 3:19pm:

DD, Might be a heat transfer thing too. I assume the seamed box was empty when you heated it and you said the Altoid one had water in it. I've heard of boiling water in a birch bark bowl too.

Yes.  That is quite possibly true.

I've also seen film of people boiling water in a plastic bottle and one of the "drills" I did as a Boy Scout (many moons ago) was to boil water in a paper bag.

So, it is pretty obvious that in those situations, much of the heat is being absorbed by the liquid rather than exclusively by the container.

dd