I just bought the PI Barrier GTX a couple weeks ago. I have yet to use them below 40F, but from what I can tell, they seem very warm. They have two separate uppers attached to the same sole. The outer one has the GoreTex, and zips up with a velcro tab at the top. The inner upper has the Thinsulate, and closes with speed laces. My only complaint is the damned velcro wants to grab my socks and tights as I'm pulling them on.