Now consider a plastic spoon in the same cocoa.

Heat moves through the plastic slowly, so the handle stays cool.

Heat moves through the plastic spoon slowly.

Now consider two hot potatoes, one wrapped in foil and one in a cloth napkin.

One hot potato in foil, one in a cloth napkin.

Metal foil is a thin sheet of metal. Heat moves through it quickly, so the outside of the foil is hot.

Heat moves through the foil quickly.

Heat moves through the cloth slowly, so the outside of the napkin stays cool.

Heat moves through the cloth slowly.

Your coat is cloth too.

On a cold day, the coat slows the heat moving out of your warm body, so you stay warm.