I recently saw a picture of expert Douglas Baldwin with his sous vide equipment in this article. One of his immersion circulator baths was covered with ping pong balls.

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What is the purpose of covering the immersion circulator bath with ping pong balls?

1 Answer 1


It is to lower the water evaporation from the bath, and keep the temperature of the bath even.

The concept has been used in chemistry labs for years! But normally, the balls are smaller and made of polythene - those are a bit big.

  • Wouldn't the circulation pump from the I.C. keep the bath temperature even?
    – Adisak
    Apr 26, 2011 at 22:09
  • 7
    The balls form an insulating layer on the surface, which is where most heat is lost if the bath is not covered. That makes the circulating heater work less hard than it would do otherwise. Apr 26, 2011 at 22:41
  • 3
    Then why isn't there a lid or something?
    – Sinan
    Apr 27, 2011 at 9:20
  • 3
    You see the ones on the left and right do have lids. The middle one just doesn't have one, so he improvises. Plus, you don't have to take off the lid to add or remove food, this way :)
    – Ray
    Apr 27, 2011 at 10:00
  • 2
    @Ray: The item on the right is a chamber vacuum. It needs to have a lid or it can't make a vacuum seal. But your other points seem valid. I have a plastic lid for my sous-vide bath that has a cut-away for the immersion circulator. Since Mr Baldwin seems to have the same kit as me (in the center with the plastic tub and the PolyScience IC) it seems he must prefers the ping-pong balls to the lid.
    – Adisak
    Apr 27, 2011 at 19:44

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