As we saw in class when a fast moving person ran into a slow moving person, the fast moving person slowed down and the slow moving person sped up.  This transfer of energy happens also on a molecular level when fast moving molecules (hotter) run into slow moving molecules (colder).  This is why the spoon in your coffee gets hot:  the molecules of the coffee (fast) hit the molecules of the spoon (slow) and speed the spoon's molecules up.  Since the coffee molecules are now going slower, the coffee cools down.

The material the spoon is made out of is a heat conductor, which means that the molecules in the spoon tend to effectively transfer their energy to their neighbors, speeding them up -- all the way up the handle of the spoon.

An oven mitt is made out of a heat insulator. The molecules in this type of material don't effectively bump into one another and transfer heat energy, so the inside of the mitt stays cool, even though the outside of the mitt is holding something hot.

Note: If something feels "cold", it means that it is conducting heat away from your body, and if something feels "hot", it means that it is conducting heat energy to your body.  Since different materials conduct heat better than others, two materials at the same temperature may feel different. For example, outside on a cold day a piece of metal will feel colder than a piece of wood, even though they are at the same temperature.  (Metal conducts heat from you better than wood.)

Coolers and can "coozies" are also insulators.  They keep the heat energy out of something you want to stay cold.  Note:  a major misconception is that coolers keep cold in.  Remember, there is no such thing as cold energy; something has a lower temperature if it has less heat energy.  Would it be a good idea to put a blanket over some ice cream if you wanted to keep it from melting?

A vacuum is a very good insulator because there are no molecules to bump into one another.  A thermos is often made of a double wall of glass with a vacuum in between.