For two days the heat index here where I live has been in the low 100's. So far I am very pleased with the Phase Change cooling vest I bought this year. Monday I spent 15 minutes outside with the temperature at 82 and had no ill effects from the heat. Yesterday and today it has gotten up to 85 in my home again no ill effects from the heat.
Today I have been timing how long my vest lasts and I'm at 4 hours already with still about 20% of the packs are frozen and my extra set of packs have been frozen in just the fridge for quite a while now. I have even gone out to mow my lawn in 82 degree weather with no ill effects and that was spending around 45 minutes outside. On Monday I wore the vest when I went to the VA and the packs were still just slightly frozen when I got home 6 hours later. But most of that time was spent in air conditioned environments.
The VA had given me the ice pack type of vest but found it too cold for me to tolerate since they freeze at 32 degrees. The phase change packs freeze at 58 degrees so it is easier to tolerate the cold. The only way I could tolerate the ice pack version was to also just put it in the fridge which wouldn't actually frees the water in them. Then it would only last about 1 hour before I needed to change packs in order to keep myself cool.
The Phase Change cooling vests are kind of expensive (~$300 with tow sets of packs), but I think well worth the price if they continue to work this good. That year I was basically trapped inside my house because of the heat. And even then I was constantly feeling the effects on my symptoms the entire summer.
Dennis