Thermal Insulation

Materials which are used to prevent the transfer of heat are called thermal insulating materials. There are three modes of transfer of heat - conduction, convection and radiation. The inside of a concrete wall which has one side exposed to outside winter temperature feels cold to the touch. Heat is being conducted from the higher  temperature to the lower temperature side of a structural member. From there it is transferred to the outside air mainly by radiation. When air is heated it expands and begins to circulate. During circulation, if it comes in contact with cooler surfaces, some of its heat is given up to them. It is therefore important to try to prevent air currents (convection currents) from being set up near about the walls and ceilings of our buildings. This can be done by keeping the circulating layer of air to be relatively thin - not over 1 in  and by dividing the space into small enclosed compartments. The convection currents set up in the confined spaces are insignificant and can cause little heat transfer. To prevent heat losses by conduction we must use the materials that are poor conductors. To prevent loss by radiation, materials must be used which will reflect rather than radiate heat.