Why are things hot or why are they not?
Hot or Cold
A thermos is also called a vacuum bottle because it uses a vacuum-a space that has no air in it-to keep heat from escaping from hot things inside; it also keeps heat from getting inside to make cold things warmer. The vacuum is located in a thin space between the thermos liner and its outer wall, where it stops the movement of heat to and from the outside air. A vacuum works in a thermos because it is empty of air (and molecules) and therefore has no conductivity. (Heat is caused by the motion of molecules.) Because the opening of a thermos is also tightly sealed with a stopper or lid made of a nonconductive material, no heat can escape or enter there, either. Hot food stored in a thermos can keep its heat for many hours; in the same way, cold food can remain cold because the vacuum insulates it from the warm air surrounding the thermos.
Read more: http://www.answers.com/topic/how-does-a-thermos-keep-cold-things-cold-and-hot-things-hot#ixzz2WfxhwARs
The Flow of Heat Energy
When you bring two objects of different temperature together, energy will always be transferred from the hotter to the cooler object.
There are 3 types of heat transfer.....
Below you will find a link that will give you more information on the flow of heat energy and the 3 main types of transfers.