I am currently building a water cooled vest for the hot days here in Phoenix Arizona. Some days in the summer can reach upwards of 115 degrees F, and I would like something to keep me alive if I go out to ride my Motorcycle or just work out in the backyard. My current design is a vest with 1/4 clear vinyl tubing laced throughout that all leads back to a 2 liter water bladder filled with a 90% water 10% ethanol solution (so I don't have to worry about algae). A 12v DC pump keeps the water moving. Inside the water bladder are removable cold packs. My question is what would stay colder longer. Cold packs filled with the same 90% water 10% ethanol or Cold packs filled with 100% ethanol My thought is, pure ethanol's freezing temp is drastically lower than pure water, -173.2°F vs 32°F. The average freezer temp is 0 °F. But pure ethanol does have a lower heat exchange rate than water. Does that mean that ethanol would keep the water slightly cooler than ice for a longer period?