Conduction is the process by which heat transfer takes place in solid matter, such as the direct flow of heat through a material within a single or two separate bodies in direct contact. Scientifically, it is the mol – ecule-to-molecule transfer of kinetic energy. One molecule becomes energized and, in turn, energizes adjacent molecules. A cast-iron skillet handle heats up because of conduction through the metal from the heat energy provided by the burner on the stove. This also occurs when a person touches a sun-warmed window or when the handle of a poker gets warm after the other end has been placed in a fire for a few minutes.
Convection and conduction are functions of the roughness of surfaces, air movement, and the temperature difference between the air and surface. Mass insulations, because of their low densities, are designed to suppress conduction and convection across their sections by the entrapment of air molecules within their structure. Convective air currents are stilled by the surrounding matrix of fibers or cells, and the chances of heat transfer by the collision of air molecules are reduced. Foam insulations operate under the same principle, although gas is used instead of air within their structure.