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Thermal conductivity of air is less than...

Thermal conductivity of air is less than that of felt but felt is a better heat insulator in comparison to air. Why ?

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In felt there are fine holes packed with air. Since the air is trapped, it cannot move. Hence there cannot be any convection in felt. The thermal conductivity of air is less than that of felt. But convection current can set up in open air, which causes the transfer of heat. So felt is a better heat insulator.
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