The vest works better in low humidity but it still works well in high humidity as mentioned by gpzrocker. I keep mine in the fridge and pack it in my topcase in a soft cooler and only put it on when I start to get uncomfortable. The cold soak does not bother me and gives me a refreshing jolt like diving in a pool..
Do not squeeze the excess water out, you may squeeze out some of the gel. This happend to my first vest and it now only holds half as much water. It still works great for a short hop but I bought a new one for longer rides. I also have an evapo skull cap and neck band. That's why I am the coolest dude in town.