I've used a partially inflated Thermarest lite seat mat as a chest protector inside a wind proof jacket in very cold windy environments and it works well when just standing around in the cold wind. If I was needing to sit down, I just inflate the lite seat a bit more then sit on it. Much more comfortable than sitting on wet grass, snow, cold rocks etc for a quick brew up. If was to begin hiking again I would just deflate it, roll it up and put it my jacket pocket. Taking of a Goretex jacket to put on a thermal jacket then putting back on the Goretex jacket can sometime be a pain in the neck especially if your brew stop lasts only 10-15 minutes.

The Thermarest lite seat is a great all round flexible bit of kit. Basically if you are having to rely on a SolaTec Aerovest for survival rather than already specifying good insulated clothing then basically you haven't prepared well enough for the weather conditions expected. A lightweight down or primaloft jacket would be much more preferable to the Aerovest.