Insulating materials 

The role of insulating materials is to minimize heat losses from the high temperature reactors. These materials have low thermal conductivity while their heat capacity depends on the bulk density and specific heat. Insulating materials are porous in structure; excessive heat affects all insulating materials. Choice of insulating materials would depend upon its effectiveness to resist heat conductivity and upon temperature. High alumina with thermal conductivity   and silica with thermal conductivity   etc are amongst others, used as insulating materials.

Ceramic fibres are important insulating materials and are produced from molten silica, titania, Zirconia etc in the form of wool, short fibres and long fibres. They have excellent insulation efficiency. They are long weight.   

References:

O.P.Gupta: Fuels, Furnace and refractory