I wear an old Kokatat as well. Never had any problems with overheating from it since I wear it only when on wild waters or during the icy season. Shallow river paddling has its advantages. Even on a hot day, wearing mine doesn't cause me to heat up all that much. That said, if you are in a kayak, try splashing water all over yourself if it gets so hot that you can't stand the idea of wearing a pfd and you can't roll. Just remember one thought: if you opt for a pfd that cannot support your body weight, you might as well not wear one. Get one that does the job and suffer through the heat. Drink lots of fluids while paddling and, as I said before, wet yourself frequently. Hmm, well ok, I didn't say it that way before...but you get my drift, eh!

Robert N Pruden