Heat insulating materials
are required to grant protection against heat and cold. These materials are
generally porous and their properties are governed not only by their porosity
but also by the nature of pores, their distribution, size and whether they are
open or closed. The materials with a greater number of fine, closed and air
filled pores are the best heat insulating materials. The bulk density of heat
insulating materials is usually below 700 kg / cubic meter and their coefficient
of heat conductivity does not exceed 0.18 k cal per m hr degree Celsius.
If heat insulating materials are properly used in building construction, they greatly reduce the heat losses to the environmental medium through wall structures and as a result of this, fuel consumption is reduced. Thus the economic efficiency of thermal insulation is very high and the investments made in heat insulating materials can be recovered in a short duration of time.
In general, it can be stated
that the low heat conductivity of heat insulating materials is due to their
air filled pores. Hence, if their efficiency is to be maintained, it should
be seen that these pores are not covered with a film of water or are filled
with water because the coefficient of heat conductivity of water is about 25
times higher than that of air. Hence heat insulating materials should protect
against the moisture.
The choice of an insulating material depends on its cost, area to be covered, standard of insulation required and the cost of heating or cooling. The thermal insulating material should be reasonably fireproof, non absorbent of moisture, able to resist attack of small insects and not liable to undergo deformation. The usual insulating materials are rock wool, slag wool, fibreboard, flexible blankets, saw dust, wood shavings, corkboard slabs, mineral wool slabs, aluminium foils, products of cement concrete with lightweight aggregates, gypsum boards, asbestos cement boards, chip boards, foam glass, gasket cork sheet, foam plastic, etc.
Materials of low density
provide better thermal insulation than those of higher density.