I would agree that polypro fleece is wonderful stuff and i have had significant success with it at alleviating hypothermia, but if you become hypothermic, it alone will not pull you out of the danger zone. You need a warmer environment, usually achieved by starting a fire. A good hot meal helps as well. The insidious thing about H is that one of the first body systems to come under attack is whatever higher reasoning capabilities you may possess, rendering you less capable of recognizing the problem enveloping you. Been down that road and it is not very nice. On at least one occasion, I am pretty sure I was wearing synthetics and little or no cotton. About the only cotton items I will carry any more are bandannas and the occasional boony hat.

Building a fire is often the difference between life and death in cold weather situations.