Yeah, this is what I?d suspected too:
Evaporating water pulls heat energy from the inside of the box decreasing the temperature an average of 10 to 20 degrees Fahrenheit from ambient conditions, and even more in dry, arid environments!
It is basically like the old trick of putting a wet washcloth around your room temp can of beer.

I agree - probably good for the right use, but I don?t know that I want it for days in the woods.