When we touch something cold or hot, our feeling does not always depend on how cold or hot the thing really is. The pen and the pencil on your table are both the same temperature, but the pen feels much colder than the pencil. All parts of a hammer are the same temperature, but the iron part feels much colder than the wooden part.
In all these cases, the object we touch is colder than our skin. So the heat goes from our skin into that object. Our feeling depends on how quickly the object takes heat from our fingers.
Iron takes heat quickly from our fingers; it makes our fingers cold, and so we say that it is cold. But wood does not take heat away so quickly from our fingers, and we say it is not so cold.
So we can say that iron is a good conductor of heat, and wood is a bad conductor.
