I've got a pair of
these guys.
The original ad I saw said that they had been designed for the Army, and that rather than generating real heat they operate at only body temperature.
I wore them a couple of times, and they did a respectable job, but they were a nuisance to work with, and they burned 4 AA batteries in about two hours.
They've sat in a drawer for the past bunch of years waiting 'til I'm next inspired to take a walk when it's down around 10º.
GORE-TEX is a good product, but Thinsulate has never made enough of a difference to make me feel like it was a good purchase, so I'll stick with my two layers unless there's a miracle product out there to which someone can direct me.