My late wife Carol loved to ride and had Mutiple Scleorsis. She could not tolerate the heat or else she would have an exerbation and it would likely put her in the hospital. She did not want to let the MS take riding away from her. So we have lot's of experience with the Veskimo. I would highly recommend them. They are a very reputable company that stands behind their product. We purchased the veskimo at first with the back pack. A lot depends on the heat, humidity, how hard the ice is and how cool the body is as to how long a "charge" will last. Generally here in North Texas in the 100+ temps in August, it would last about 2 hours then we would have to more ice in it. We decided to get the 9 quart cooler. We have a deep freeze with the temp set at -20*F. We made our own block ice using some tupperware containers. I could put two blocks of ice in the 9 quart cooler and cold water from the refrigerator, temp around 37*F, and the charge would last around 6-8 hours. Carol liked wearing a t-shirt under the veskimo then a leather vest over the veskimo. Even in August, the temp inside the leather vest was in the mid 70's. I have tried to use it, when I do, I have to circulate the pump on and off because I get to cold wearing it, even in August!!! If you go to their web page http://www.veskimo.com/cooling-vest-ms-medical.php that's Carol modeling it for them and our side car rig. I have it wired up to the bikes electrical and when she was on her scooter we ran it off the battery pack with rechargeable AA batteries.