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what's the gel made of inside a pressure activated cooling pad? Answered

I'd like to know what the GEL is made of inside those clever cooling pads sold as mattress cooling pads and pet cooling pads. And, can I make my own version for my dog at a considerably reduced price from the on-line stores? I don't want the freezer gel recipe,(water and rubbing alcohol), I need the pressure activated type gel recipe. THANK YOU INSTRUCTABLES COMMUNITY

16 Replies

Jack A LopezBest Answer (author)2013-06-08
I'm going to take another stab at this.

I am guessing the magic gel you seek is better described as a "phase change material", and that it is not truly "pressure activated", although for some reason that phrase is often used to sell it.

For those just joining the discussion who have never seen or heard of such a "pet cooling pad", I am guessing these links,
are examples of the product OP is asking about.

Both those pages are selling a "cooling pad", or "cooling mat", said to be  "pressure activated".

However, take a look at this page,
 a wholesaler profile page for Hangzhou Phase Change Technology Co., Ltd.


These pages are using the word,  "phase change material",
to describe their product.

The phrase "phase change material" (PCM)  might sound like something complicated, however I claim these materials are all analogous to melting water ice.  The differences being that the magic PCM has a different "melting" (phase change) temperature, and also a different value for the latent heat, amount of heat absorbed per unit mass of material, than water ice.

I put quotes around the word "melting", because the actual phase change might not look like melting; i.e. solid before absorbing heat and liquid after.  In fact both the before phases might look to be solid, or squishy gel, or whatever.

I am trying to guess what would be a good choice for a non-toxic PCM, if you wanted to, uh... roll your own, PCM based heat absorbing mat for your dog.

The trick to doing that is going to be finding a PCM with an appropriate phase-change temperature.  This is in phase change temperature analogous to melting point temperature for water ice.  That is to say a box of melting water ice keeps a constant temperature of about 0 C.  But you want  a material that will "melt" at more like 25C, so it can cycle between the temperature of your dog, at like 35 C, and the temperature of the room at maybe 20 C.  

To say that another way:  Your dog  is hot enough to "melt" this material, thus putting latent heat into it.  The room is cool enough to re-"freeze" the material, thus taking latent heat out of the material.  

I remember from reading the Wikipedia article on sodium sulfate,
this material mixed with water, or mixed with water and sodium chloride, had a phase-change temperature(s) maybe close enough for your dog cooling application.  It's probably worth it just to re-paste that whole blurb here.  I put some bold emphasis on those two phase change temperatures.

The high heat storage capacity in the phase change from solid to liquid, and the advantageous phase change temperature of 32 °C (90 °F) makes this material especially appropriate for storing low grade solar heat for later release in space heating applications. In some applications the material is incorporated into thermal tiles that are placed in an attic space while in other applications the salt is incorporated into cells surrounded by solar–heated water. The phase change allows a substantial reduction in the mass of the material required for effective heat storage (the heat of fusion of sodium sulfate decahydrate is 25.53 kJ/mol or 252 kJ/kg[19]), with the further advantage of a consistency of temperature as long as sufficient material in the appropriate phase is available.

For cooling applications, a mixture with common sodium chloride salt (NaCl) lowers the melting point to 18 °C (64 °F). The heat of fusion of NaCl.Na2SO4·10H2O, is actually increased slightly to 286 kJ/kg.

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candi_m (author)Jack A Lopez2013-09-05

I was thinking of getting one of these cooling pads for my dog, particularly one from Green Pet Shop. Even though it says it is non-toxic I still worry. Any idea on how to figure out if a dog got into the pad and actually ate the gel, could it cause serious problems for the dog, possibly even death?

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ChrisD286 (author)candi_m2016-06-28

yes, these pads can cause death. 4 reported cases by the animal poison control of dogs eating this gel substance and suffering sever neurological damage

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Jack A Lopez (author)candi_m2013-09-06
I don't think this pet cooling pad is likely to poison your dog, provided it is made out of what I think it's made out of, i.e plastic, water, sodium sulfate, and maybe sodium chloride.

I mean there are things capable of poisoning dogs, like antifreeze, raisins, chocolate... I tried using Google(r) to see if someone compiled a list, and I found this:

Of course, I am not the person who should be trying to reassure you.  I am not an expert regarding dogs, or chemistry, or materials science.  Mostly what I do here, in the Answers forum, is use Google(r) and Wikipedia(r) to research people's questions, and then report back what I find.

Try writing to thegreenpetshop.com, and ask if they have any documents, like a MSDS or similar, certifying what is in their pet cooling pad, or certification that whatever it is, is in fact non-toxic, safe for dogs to eat it, or whatever.

Some kind of certification/documentation probably exists,  and the reason I suspect that is from looking  at a page like this one,
This is a page from a wholesaler,  and there's  a little blurb that says,
"FDA,SGS,CE,MSDS authentication"
and I am guessing that blurb refers to some kind of documentation, from some authority or authorities, saying something.

So if you ask for these certificates, you'll probably find someone who can retrieve them for you.  Of course if they don't have any of this paperwork, or are not willing to share it,  you could just ask one of these friendly sales associates if he or she would be willing to eat some, or all, of the contents of one of their pet cooling pads. 

It would probably have to be somebody in management, to find someone crazy enough to do that.  But it is supposed to be non-toxic, right?

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Kiteman (author)2013-06-07

If you want to make one pad, from scratch, it is unlikely that you will be able to match the cost of a commercial product like that, purely because of economies of scale.

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rickharris (author)Kiteman2013-06-08

Why not just put a small zip loc bag 2/3 full of water in the fridge to partially freeze.

You could mix a small amount of antifreeze in to prevent hard ice forming & just get it slushy.

Put in a cloth to prevent freezing the flesh.

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TerryS83 (author)rickharris2016-05-28

antifreeze is highly toxic to animals. less than a teaspoon can kill a dog in hours. cats only need a drop. please do not ever use antifreeze anywhere around animals.

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rickharris (author)TerryS832016-05-29

antifreeze comes in many forms, Alcohol for example. However I take your point.

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lauren1985 (author)2014-07-11

I went to the green pet website, and found the patent number, searched it, and here you go: http://www.google.com/patents/US8720218

4. The cooling platform of claim 3 wherein the pressure portions include a means for inflating and deflating.
5. The cooling platform of claim 4 wherein the pressure activated recharging cooling composition is comprised of:
thirty percent carboxmethyl cellulose;

twenty percent water;

thirty-five percent polyacrylamide; and

fifteen percent alginic acid.

6. The cooling platform of claim 1 wherein the support layer is comprised of memory foam.
7. The cooling platform of claim 1 wherein the channeled covering layer comprises a piece of fabric or net covering.
8. The cooling platform of claim 1 wherein the angled segments within the sealed perimeter are sealed.
pretty cool!
maybe hard to make at home.

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1way2go (author)2013-06-11

WOW! This is EXACTLY what I was looking for! Thank You Jack A Lopez! You've taken the mystery out of this product. As a visual analogy of what you described as phase change at higher temperatures, I remembered observing my large jar of coconut oil recently, (purchased from Costco), that it stays SOLID at temperatures up to the low to mid 70'sF. And when temps get near 80F it turns to liquid. I feel like I've learned a lot from your post! However I now see that I am over my head at trying to make my own. As Kiteman said, it's cheaper to buy one of those pet pads at a retailer than to re-create my own from scratch.
...LOVE me some Instructables

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Jack A Lopez (author)1way2go2013-06-13

Glad I could help shed some light on how the dog cooling mat works, even if I don't have an exact recipe for the PCM mixture contained therein. I think part of the mixture is hydrated sodium sulfate, and I found some patents related to that,

Although, like you say, it is looking like the cheaper option for this dog cooling mat is to just buy one of the mass-produced ones.

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Jack A Lopez (author)2013-06-08

I do not think I have seen the exact product you describe, specifically a pad for cooling a pet, or for cooling a mattress. If you have link to a picture, or page with someone selling one of these things, that would be helpful.

I have seen something commonly called an "instant cold pack"

Like the Wiki article says, the cooling mechanism is based on an endothermic reaction.  Usually the reactants are dry ammonium nitrate and water, although I have also seen instant cold packs containing dry urea and water, which gives similar results.

The result is, after the ingredients are mixed, you get ammonium nitrate dissolved in water, and it's cold.

Theoretically you could recycle, or re-build, reactivate, one of these cold packs simply by re-drying the ammonium nitrate, i.e. by boiling off the water and drying the resulting crystals.  Then mixing those dry crystals with new water would give you the original heat-absorbing (i.e cold producing) reaction.

Of course most folks just use an instant cold pack like this once, and then throw it in the trash, which is exactly the manner in which it was intended to be used. 

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rickharris (author)2013-06-07

Sodium acetate - you CAN make this see link


BUT the overall cost is probably lower to just buy one.

All the ones I have had have leaked sooner or later - generally sooner.
I prefer a bag full of wheat grain heated in the microwave.

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Kiteman (author)rickharris2013-06-07

That's for a heating pad - the author asked about cooling pads.

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rickharris (author)Kiteman2013-06-07

agggg must read more carefully - write out 100 times!

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