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Insulation vs heat barrier

  1. Sep 29, 2009 #1
    Sorry for such a simple question, but what are the differences between using insulation and heat reflective material? What is the effective of using them together?

    In my case I want to shield flammable foam insulation from melting or catching fire from a nearby heater. Will covering the foam with heat reflective film help?

    Thank you.
     
  2. jcsd
  3. Sep 29, 2009 #2
    Yes it will help, but only against the thermal infrared radiation. There are three parts to heat transport, radiative and through heat conduction and through convection.

    1) The radiative part scales with T^4 as far as I remember so it gets very large for things like fires. This is also why stove plates glow in the dark. The infrared radiation can be reflected to some degree with metal foil.

    2) Then we have heat transport, which can be reduced by using a bad thermal conductor. The way to think about this is that the material which you want to protect is connected to something cold like the outside air or a wall by a better heat link then that to the heat source, or that the heat source is not turned on long enough that appreciable heat could be transferred.

    3) Convection, the most important part. Air is really a poor heat conductor, but if we move the air, it will take the heat with it. The main part of almost all household insulation is making sure that air doesn't move. Multi layer clothing, foams (they are just trapped air), glass wool, all things to keep the air from flowing from hot to cold.

    So yes metal foil helps. A few layers with air in between even more. But if you want to build something so your house doesn't burn down when your are asleep, I would think about flame retardant insulation. Every f-ing carpet sold today must show this property...
     
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