I friend of mine tried floating, where you lay in a bath kept at body temperature (98.6 degrees F). He said after a while you don't feel the water at all.

This made me wonder why being in warm water (bathtub, spa, etc) is comforting, but a hot weather feels miserable. Can someone explain the difference?

  • $\begingroup$ I think it is subjective phenomenon. $\endgroup$
    – Dexter
    Nov 4 '15 at 12:14
  • $\begingroup$ I don't know about you, but I can walk around in only a T-shirt when the air temperature is 10°C, but jumping into 10°C water is going to be a world of pain... This should really be a chemistry or physics question about specific heat capacity. $\endgroup$
    – AMR
    Nov 6 '15 at 1:56

You constantly generate heat from metabolism. The ability of this heat to be transferred to your surroundings from your skin is tremendously different in air vs. water. This is known as thermal conductivity.

The ability of water to remove heat from your skin is roughly 24 times that of air. See list of materials and their thermal conductivity rates here

In water of close to body temp, you can still bleed off heat to water. Your ability to do so in air that is close to body temperature is greatly reduced, so much so that in order to keep up, you sweat and increase the cooling ability through the evaporation of that sweat at temperatures well below 98.6F.


Hot air generally has lesser moisture hence increasing the loss of moisture from our skin. Note that a sauna bath does not feel as uncomfortable.

Also while conductivity of water is grossly more than air (thermal) One has to take into account convection of hot air which may increase the total heat transfer from air to the body.

  • $\begingroup$ In case of floating. The question. Is where does the 90 watts of basal heat go... Obviously conduction does not take place without temp gradient...Prespiration .... Will it be possible ? $\endgroup$
    – ARi
    Nov 5 '15 at 18:39
  • 2
    $\begingroup$ The specific heat capacity of water is also huge...If you were in a tank with 100's of gallons at exactly 98.6, and it was perfectly thermally insulated to not decrease...it still would take a long time for your 90 watts to raise the temperature appreciably. And even if it was exactly 98.6, and your body temp raised to 99 because of no gradient...voila, now have a gradient. $\endgroup$
    – akaDrHouse
    Nov 5 '15 at 23:57

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