Do cooling coats work?

It's that time of year when those folk that do performance dog sports (especially agility and flyball) have to start keeping an eye on the outside temperature and their dogs' comfort level in the heat. Many people suggest the use of cooling coats to keep their dogs cool, and there are a variety of coats available.

I've taken a look at a few of the available offerings here  in the UK with some thoughts on how helpful or otherwise they are likely to be. I should probably say up front that I'm not a physicist past GCSE so all my comments on evaporation etc are subject to that caveat - don't take what I have to say as gospel - and if anyone out there has a counter viewpoint I'd love to hear it.

While writing this article, I reviewed the following coats:

Prestige Dog Cooling coats
Ruffwear Swamp Cooler
Hurtta Motivation Cooling Coat
Easidri High Performance Cooling Coat

I also looked at the Chillax Mat, which acts on the less-furred areas of dog, and therefore will provide more cooling capacity due to its proximity to major blood vessels when the dog is lying down.

On cooling coats in general, I have to admit to a certain degree of skepticism. If we consider the advice given regarding treating dogs with heat exhaustion (such as advice given by Cani-X) it is generally "don't cover the dog, even with wet towels". This is due to the "sauna effect" whereby convection is inhibited, and instead the air around the animal, between its coat and the covering, heats up. It's hard to see why advice for prevention would be fundamentally different from advice for a dog that's suffering.

Even leaving aside the sauna effect, a dog's coat is supposed to act as an insulator. Some are more effective at this than others (those with double coats having a better chance at temperature regulation, at least to begin with,  than those very smooth coated breeds) . It's easy to forget that those "well-insulated" dogs are insulated against the heat, as well as the cold. The air trapped in the double coat can act to keep the heat in (when it's cold) or the heat out (when it's warm). By adding another layer on top of the coat, heat then has to work from the dog's skin, through the air trapped in the hair, through the air trapped between the hair and the cooling coat, through the coat to the outside.  Good if it's cold and we want the heat to stay in as long as possible, not so good if it's warm and heat needs to be moved away from the skin as rapidly as possible.

Another reason that I'm not convinced about the efficacy of cooling coats is that the major routes for cooling a dog are via evaporation of saliva from the tongue and mouth, via the merocrine glands in the paws and through convection/evaporation under the body, where major blood vessels run close to a surface that has less fur on it (groin, throat and armpits). There is a lesser effect from dissipation of heat from the skin (via the air in the coat) to the environment. So it makes sense to maximise heat dissipation from the major routes, while not worrying too much about the minor route. And just about every cooling coat focuses on covering the back - where the dog's fur is thickest.

All of this said, I definitely do think cooling coats have their uses. If the dog has a finer coat, such that the insulating effect is lost and the heat from the skin can easily be drawn along the temperature gradient from skin to cool coat, that will cool the dog down more rapidly. In addition, if the coat is used as a mechanism to bring down the air temperature around the dog, then removed so there is no sauna effect that might also be effective. Finally, if the coat in question is an "active" cooling type (though I didn't find any of these in the UK - only the USA) and have reflective properties so that either the sauna effect is disrupted and the heat is continually drawn off the dog's body, without the air around the dog heating up, or some of the sun's rays are reflected back, away from the dog I can see that this mechanism of action *might* overcome the downside to being covered in an extra layet.

It does seem a pity that no one has yet been able to conduct an appraisal under test conditions, using a variety of breeds and taking the test dogs' core temperatures while wearing coats that work in different ways to provide any kind of conclusions on the efficacy of these items.
This video from Easidri shows clearly that the surface temperature of a dog wearing a coat is lower than one not wearing a coat, but that doesn't really help us know whether the dog's core temperature has dropped significantly.



Without evidence to the contrary, I would advise people considering using a cooling coat to instead make sure their dogs have access to water to lie in (such as in a paddling pool, or even by using a plastic mat and puddling water onto it), as this appears to be more effective for the dog than covering it with a wet coat.

Updated to add: A physics-minded friend has observed that if the cooling coat is thick enough (ie the water reservoir is large enough) then convection can continue to take place within the water and the water reservoir will act as a heat exchanger - water warmed by the heat coming off the dog will move away from the dog and towards the surface of the coat, where evaporation will take place. That cooled water can then circulate back to the dog and "pick up" more heat. So rather than getting the hot layer "stuck" between the skin and the coat, the temperature gradient will always be maintained from hot dog to cold (or at least, less hot) coat, which should transfer heat away from the dog more rapidly than just environmental effects.
So then the question becomes "how much of a water reservoir is needed for this to happen, and is there sufficient capacity in the majority of cooling coats". Given their average thickness and absobency I'm not totally convinced, but open to having my opinion changed if there's enough data out there to do so.