Sounds like it could or should be pretty heavy to put on the horse in the first place.
Now if this was a "cool suit" like race care drivers wear...for that you need tubes, wires, cooling gel, ice and a source of current.
You're talking about putting a "soaking" blanket on a horse and it cooling them???
Think about that.
If you bathe your horse it is recommended you then scrape the excess water off so it doesn't
super heat and become a heating element not a cooling & refreshing experience.
I would think this "blanket" thing would work along the same principle.
I agree with LHP....save the money.
Go rinse the horse, scrape the moisture and allow the horse to "fluff" their coat to cool same as they fluff their coat to gain insulating warmth... jmo...