I have read on the wikipedia article on superheated steam that superheated steam has the same thermal conductivity as the air and so it is athermal insulator.

Does anybody knows the reason for this?

  • $\begingroup$ look up "thermal diffusivity" on wikipedia. -NN $\endgroup$ Mar 5 at 6:23
  • 1
    $\begingroup$ Do you understand why air is considered to be a thermal insulator? $\endgroup$
    – Bob D
    Mar 5 at 9:14

1 Answer 1


Gases are poor thermal conductors compared to liquids and solids because of the distance between molecules.

The thermal conductivity of air is about 0.026 W/m.K. Superheated steam is also a gas, specifically H$_2$O gas, with a thermal conductivity of about 0.06 W/m.K. Compare these to plastics which have an average thermal conductivity of about 0.250 W/m.K (an order of magnitude greater than air).

That said, gases are only good thermal insulators if they are not free to move where they can transfer heat by convection. One thing that makes foam a good insulator is they contain trapped air bubbles.

Hope this helps.


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