Thanks everyone!
There are various cooling coats on the market. There are four basic types - metallic mesh, chamois, gel and evaporative cooling. Ilsa's vest is made by Ruffwear, and uses the evaporative cooling system.I've never heard of these cooling jackets. Do you have a link to anywhere that explains how they work and so forth?
Basically, Ilsa's vest cools the dog in a few ways. First, it's light blue and semi-faceted to reflect heat and UV. Second, it is dual layered so it forms a layer where cool air can circulate. Third, the coat is highly absorbent, and when soaked with cold water it actually pulls the heat away from the dog - it works in the same way our sweat does, as it evaporates, it cools.
Link to Ilsa's vest
The mesh kind are very expensive, I've only seen them at dog shows, and all they do is reflect the sunlight.
The chamois kind are in vogue with the show folk right now, but they're heavy when wet and not well-suited for hiking. Now if the dog is being led around the show grounds, they work well. They do keep cold for much longer, and can be used in emergency cooling situations because they can be removed and balled up, and placed on the head or between the rear legs to provide emergency cooling.
Link to chamois cooling coats
And the gel kind... not even worth mentioning. Basically there are absorbent gel balls inside the coat, and when soaked with water they swell. They dry quickly, and the gel balls move around, creating large areas where the dog isn't being cooled at all. This is the method the "cooling bandannas" at Petsmart use... useless IMO.