Thermal conductivity

The easiest way for heat transfer is thermal conductivity. In thermal conductivity the higher energy is transported from one molecule to another and thus conducted throughout the material. Heat transfer only takes place from areas of higher temperatures to areas of lower temperature.

The ability to conduct heat is different from one material to the other and depends on how good the material can transport the energy. This is measured with the guide number.
The guide number specifies the amount of heat that can be transported through the opposite sites of a cube with the edge length 1. The difference in temperature must be at 1 K.
Metals for example have excellent thermal conductive characteristics. However, gases, wool or paper have worse conductive characteristics. The bad thermal conductors are also called heat isolators.