A Hydration Hose Cooling System.
With all the various accessories available for hydration systems, I needed to create one that I have not found available from any vendor.  Once I started backpacking with Boy Scouts in the summer I had to switch to a hydration bladder. This allowed me to avoid dehydration by taking periodic short sips without breaking stride.  I found, however, the water I was sipping to be very warm. As I suck on the mouth piece I would eventually hit the cooler water that was coming directly from the bladder inside my backpack. By that time I hit the cooler water but I had finished drinking.  When it came time for another sip, the new water in the hose was again heated up.  On a day in the high 80s or low 90s, I would estimate the temperature of the hose water to be about 10 or 15 degrees hotter than the temperature of the bladder water.

While there are accessories to prevent water in the hose from freezing, I found nothing that would help with this situation. Indeed, if you were to use the available black foam covering that prevents freezing, in the summer, it would likely make the problem worse.

What I have done is create a tight fitting sleeves for hydration hoses out of strips of a white terrycloth towel.  I start out with this towel sleeve wet and whenever I pass a water source I simply dunk that section of the hose in the water making sure to protect the mouthpiece from the untreated water.

This set-up works in a way similar how the old "Saturate before using" safari canteens worked.  As the water on the towel evaporates, the water in the hydration hose is cooled.  While it takes only 1 calorie of heat to raise one gram of water 1 degree Centigrade, it takes 539 calories to evaporate that same gram of water.

How well does this work?  I estimate on that same 80 to 90 degree temperature day, instead of the water in the hose being 10 to 20 degrees warmer than the water in the bladder, with this wet sleeve in place, it is now 10 to 20 degrees cooler.  Drinking water that's now 20 to 30 degrees cooler can be a real asset on a hot summer trek.

I dont know if its the 5 different backpacks ive tryed or just my very thin frame which doesnt sit well with different pressure points on backpacks because of my lack of meat but my girlfriend and i would like to see some kinda pad that runs around the back of your neck from shoulder to shoulder and connects the 2 backpack shoulder straps kinda like the one that connects near your sternum cept higher in the back and with a wide pad that contours to the base of your neck and tops of your shoulders for more surface area and less pressure on shoulders. ill be stoked if i see an add on REI website for a new and improved backpack after this.:)