Ahhh... but the humidity under the lid is as close to 100% as you can get in an unsealed environment, thus all but prohibiting additional evaporation.

Now my head is spinning a bit... what you say does sound as true... but it makes me wonder, how much of a difference would the presence of a tiny hole in the lid make regarding heat preservation?

 

Now my head is spinning a bit... what you say does sound as true... but it makes me wonder, how much of a difference would the presence of a tiny hole in the lid make regarding heat preservation?

There will be some convection in the vicinity of the hole. Hot, humid air will rise out, cool dry air will fall in. The rate, though, will be *much* slower than an open container.

More importantly, I think, is the heat released to the lid (and then convected away from the other side of the lid) due to condensation of water vapor under the lid.

 

I recall a colleague of mine buying one of these things and telling me that it keeps hot things hot, and cold things cold.

I then asked him what he had in it.

He replied two cups of coffee and a choc-ice.