I recently bought a pressure activated gel cooling pad for my dog.

(comparable product: https://www.amazon.com/Hugs-Pet-Products-Pressure-Activated/dp/B00C65TXO6)

The mat is filled with a gel that noticeably cools down, when light pressure is applied. Now, in my understanding compression should lead to an increase in temperature.

Unfortunately I was not able to find any sources that explain the effect involved in pressure induced cooling of the gel inside the cooling pad. I could also not find any further information about the gel itself that is inside the cooling mat.

Can someone explain to me how such a cooling pad works and what the physics are behind it? I would also be happy if someone could point me towards any literature on this topic.

  • $\begingroup$ Does the compressed gel feel any colder than an adjacent chunk of metal? If not, it sounds like the mechanism could simply involve improved thermal contact to a thermally conductive material. $\endgroup$ Jul 7 '21 at 14:06
  • $\begingroup$ That is a very good point. It does actually feel comparable to an adjacent piece of metal. However everything I can find explicitly mentions that the gel is pressure activated. $\endgroup$
    – user306429
    Jul 8 '21 at 15:55
  • $\begingroup$ Note that all thermal conduction between objects is pressure activated. But it does seem that Carl Witthoft has a more accurate description of the actual mechanism. $\endgroup$ Jul 8 '21 at 16:09

As you might expect (well, if you have a background in chemistry or materials science anyway), here's the basic cycle

The gel in a cooling pad is water-based with a polymer. Polymer is an activated chemical that changes properties when pressure-activated. When it’s activated it pulls the heat from the body. It is based on endothermology which means a chemical change that is accompanied by an absorption of heat.

How does Polymer Activate? When contact or pressure is removed and there is no longer heat to absorb, the pad re-activates. It typically takes 20- 30 minutes depending upon the environment. … To reactivate the cooling pad, simply remove from pressure and let it sit in a cool place for approximately 30 minutes.”

  • $\begingroup$ In other words, it's a dry puddle of water which doesn't evaporate which is both good and bad. $\endgroup$
    – DKNguyen
    Jul 7 '21 at 16:04
  • $\begingroup$ Unfortunately I am not too familiar with the thermodynamics of polymers, but what exactly happens, that makes the polymer able to absorb heat by applying pressure? Is it actually a form of second order phase transition, as the above comment implies? Also what is endothermology? A quick search did only show that term in the context of other cooling gel products. $\endgroup$
    – user306429
    Jul 8 '21 at 15:41

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