i've tried a few but really have not had much relief from this texasheat!
i've used the kind you wear over your shirt with the freeze chargable innserts.
nike made a really cool cooling vest for the summer olympians a few years agobut i was never able to locate one - they looked like tthey would really keep your core temp down.
since then, i stay indoors mostly. i'll use a cooling bandana which helps for 20 minutes or so
i've found that milkshakes or icees help restore my foggy vision within a minute or 2 - just make sure going to the bathroom often isn't going to be a problem
i hven't looked around at vests in a year so if i find a decent one i'll loet you know!
If you can't explain it simply, you don't understand it well enough. - Al Einstein